Charging Lithium Batteries: The Basics. 100ah battery charging current

Sealed lead acid SLA battery charging and flooded lead acid battery charging technologies

  • Coulometric Efficiency
  • Minimum voltage
  • Cyclic versus Standby charging
  • Temperature compensation
  • Unregulated Transformer-based Chargers
  • Taper Charging
  • Constant Voltage Charging
  • Constant Current Charging
  • Fast Charging Options
  • Three step chargers

Lead acid batteries have come a long way. They have an incredible number of man-hours in research, science, and manufacturing technology. The high voltage, robustness, infrastructure and low cost will make sure they stick around for a long time.

Weight We have visited at least 10 factories in China. One interesting thing that I learned is that you can judge a sealed lead acid battery by its weight. They said If you want a cheaper battery, no problem, we will just use thinner plates and less lead. Of course the thinner plates will fail faster and give less lifetime. That is the trade-off. All the battery factories in China run off the same basic profit margin, so if the battery is significantly cheaper, now you know why. You can judge the quality of a sealed lead acid battery by its weight.

Coulometric Efficiency. This is the efficiency of battery charging based solely on how many electrons you push in. If you compare watts in to watts out you have to take into account that the battery charging voltage is higher than the battery discharging voltage. The coulometric charging efficiency of flooded lead acid batteries is typically 70%, meaning that you must put 142 amp hours into the battery for every 100 amp hours you get out. This varies somewhat depending on the temperature, speed of charge, and battery type.

Sealed lead acid batteries are higher in charge efficiency, depending on the bulk charge voltage it can be higher than 95%.

Minimum voltage

Anything above 2.15 volts per cell will charge a lead acid battery, this is the voltage of the basic chemistry. This also means than nothing below 2.15 volts per cell will do any charging (12.9V for a 12V battery) However, most of the time a higher voltage than this is used because the battery will accept higher currents, enabling the charging reaction to proceed at a higher rate. Charging at the minimum voltage will take a long long timeover 200 hours. At 2.25V per cell (13.5) it would take 85-120 hours to fully charge. As you increase the voltage to get faster charging, the voltage to avoid is the gassing voltage, which limits how high the voltage can go before undesirable chemical reactions take place. Charging voltages range between 2.15V per cell (12.9V for a 12V 6 cell battery) and 2.35V per cell (14.1V for a 12V 6 cell battery). These voltages can be applied to a fully charged battery without overcharging or damage, since they are below the gassing voltage, and cannot break down the electrolyte. If the battery is not fully charged you can use much higher voltages without damage because the charging reaction takes precedence over any over-charge chemical reactions until the battery is fully charged. This is why a battery charger can operate at 14.4 to 15 volts during the bulk-charge phase of the charge cycle. Using modern precision chargers allows both a fast charge and safe floating voltages, allowing them to be left on the battery continuously.

6V batteries need to stay below 7.1V to avoid gassing, and typical charge voltages are 6.9V (float) to 7.5V (bulk charge).

The basic lead acid battery is ancient and a lot of different charge methods have been used. In the old days, when voltage was difficult to regulate accurately, flooded lead acid batteries were important because the water can be replaced. The lead acid chemistry is fairly tolerant of overcharging, which allows marketing organizations to get to extremely cheap chargers, even sealed lead acid batteries can recycle the gasses produced to prevent damage to the battery as long as the charge rate is slow. We offer a range of chargers from inexpensive to very sophisticated, depending on the requirements of the customer, but all of the chargers we sell off-the-shelf are highly regulated sophisticated chargers that cannot overcharge the battery.

Cyclic versus Standby charging.

Some lead acid batteries are used in a standby condition in which they are rarely cycled, but kept constantly on charge. These batteries can be very long lived if they are charged at a float voltage of 2.25 to 2.3 volts/cell (at 25 degrees C) (13.5V to 13.8V for a 12V battery). This low voltage is to prevent the battery from losing water during long float charging. Those batteries that are used in deep discharge cycling mode can be charged up to 2.45 volts/cell (14.7V for a 12V battery) to get the highest charge rate, as long as the voltage is dropped to the float voltage when the charge is complete.

Voltage table for cyclic use charging. The higher voltages (above the gassing voltage) should only be used on flooded batteries that can have the water replaced:

Battery Temperature Charge Voltage per cell Charge Voltage for a 12 Volt battery Gassing Voltage per cell Gassing Voltage for a 12V battery
-20 °C 2.60 16.02 to 16.56 2.97 17.82
-10 °C 25.1 15.66 to 16.2 2.65 15.9
0 ° C 2.45 15.3 to 15.9 2.54 15.24
10 °C 2.41 14.94 to 15.54 2.47 14.82
20 °C 2.37 14.58 to 15.18 2.415 14.49
25 °C 2.35 14.40 to 15.00 2.39 14.34
30 °C 2.33 14.22 to 14.82 2.365 14.19
40 °C 2.30 13.86 to 14.46 2.33 13.98
50 °C 2.26 13.5 to 14.10 2.30 13.8

Voltage table for standby use charging:

Battery Temperature Charge Voltage per cell Charge Voltage for 12V Battery Gassing voltage
-30 °C 2.44 14.6
-20 °C 2.34 to 2.38 14.04 to 14.28 2.97
-10 °C 2.32 to 2.37 13.92 to 14.22 2.65
0 °C 2.30 to 2.35 13.8 to 14.1 2.54
10 °C 2.28 to 2.33 13.68 to 13.98 2.47
20 °C 2.26 to 2.31 13.56 to 13.86 2.415
25 °C 2.25 to 2.30 13.5 to 13.8 2.39
30 °C 2.24 to 2.29 13.44 to 13.74 2.365
40 °C 2.22 to 2.27 13.32 to 13.62 2.33
50 °C 2.20 to 2.25 13.2 to 13.5 2.30

Note that a fully discharged battery has very little sulfuric acid in solution, and since it is mostly water it will freeze solid at about 0°C, a fullycharged battery has concentrated sulfuric acid as the electroylte and freezes about.72°C. This is why a discharged battery won’t take a charge in sub-freezing weather.

Unregulated Transformer-Based Chargers

These are the absolute cheapest chargers around. They used to be very common when semiconductors were expensive and regulation was complicated. They consist of a wall-mount transformer and a diode. The transformer is designed to deliver 13 to 14 volts over a reasonable current range. The biggest problem with this approach is that when the current tapers off, the voltage raises to 15, 16, 17, even 18 volts. These high voltages can force electrolysis of the water in the battery’s electrolyte. These unregulated chargers must not be left to trickle or float-charge a battery, they should be disconnected when the battery is fully charged. This is not a problem with flooded batteries as long as you check the water periodically and refresh it. Sealed lead acid batteries can recycle the generated gasses as long as they are being overcharged at less than C/3. However, PowerStream’s testing has shown that leaving the battery to be overcharged even at C/10 (a 10 hour charge rate) will corrode the plates if left on for weeks at a time.

The transformer is so designed as to limit the current while the battery is in absorption mode. As the battery voltage rises the current decreases to top off the battery. Because the transformer is used to control the current and voltage these chargers are typically heavy and get hot

Note to our OEM customers: even though we support our OEM customers with unregulated transformer chargers to help them stay cost competitive, many of our new customers come to PowerStream because someone else sold them an unregulated charger without explaining the trade-offs, and the end-user complaints forced them to look for a better charger. Most of the time the complaints come from commercial customers rather than consumer customers. We prefer to offer the inexpensive, precise, regulated chargers that use switchmode power conversion.

Taper chargers

Another inexpensive way to charge a sealed lead acid battery battery is called a taper charge. Either constant voltage or constant current is applied to the battery through a combination of transformer, diode, and resistance. The unregulated chargers mentioned above are taper chargers. A better, and not very expensive, alternative is a regulated taper charger. These don’t let the voltage climb higher than the trickle charge voltage, so they can be also be used to maintain a battery. They won’t damage the battery if left on charge too long (even when left on the battery permanently), and they don’t change their charging characteristics if the line voltage should change.

Regulated taper chargers are very useful when you need a 12V or 24V battery backup. A taper charger in parallel with the battery, in parallel with the load makes an effective battery back-up. You should take care to ensure that the taper charger is designed to give continuous current equal to the load plus some left over for battery charging. It is also important that the current limit of the taper charger is the voltage-cut-back method, and not the hiccough method or other PWM methods. An example of suitable switching type regulated taper chargers that can be used in battery back up applications is here

There are two ways to make a regulated charger. The first is to use a transformer and a linear voltage regulation circuit. This has the disadvantages of weight and heat, but it is still inexpensive. The second uses a modern switching power supply in a wall mount or desk mount package. These low-power high-frequency switchers are surprisingly cheap, efficient, and small. They are rapidly taking over the overnight charging requirement in consumer equipment. An example of a switching-type taper charger is here.

Constant current chargers

A more sophisticated and not much more expensive charger uses an electric circuit to control the charging current. This method is useful for recovering batteries that have suffered from extensive storage without charging, but is capable of overcharging a battery if there is not some voltage limiting function, usually from the transformer. For this reason these chargers are limited to slow charging. This charger will switch to a constant-current mode when desulfating is necessary, and to a multistage precision charger at other times.

Constant Voltage Chargers (Taper plus current limit)

A circuit that is set for the maximum allowable charge voltage, but has a current limit to control the initial absorption current can produce a very nice charger. This type of charger can both charge at a reasonable rate and maintain the battery at full charge without damage. Not all constant voltage chargers are made equal, however, because the maximum voltage is a function of temperature. A temperature compensated charger is a little more expensive, and should be used where the temperature varies significantly from room temperature and the battery is on float permanently. The large chargers at An example of a switching type taper charger is here are constant voltage chargers.

Pulse chargers

I have a 3-inch binder full of pulse charging patents, the earliest from around 1900, which used a motor to spin electrodes to do the necessary pulsing. The early patents were trying to remove the bubbles from the plates of flooded cells that were being overcharged due to total lack of voltage control of chargers of that era. We have designed and experimented with pulse chargers, and haven’t found any advantage over a modern desulfating charger. Some patents show a different crystal structure formed when pulse charging versus DC charging, which is interesting, but not necessarily relevant, particularly for modern absorbed-glass-matt batteries.

Fast Chargers

Fast chargers are higher power units, designed to charge in less than 4 hours. These chargers require active charge termination and often have advanced features such as battery test, bad battery recovery, and automatic maintenance. It is safe to fast-charge all lead acid batteries with modern fast charge algorithms.

Typical Charging curves for PowerStream quick chargers.This charger starts at 8 amps and maintains a near-constant current until nearly full.

This is the fundamental algorithm of the PowerStream quick chargers for lead acid batteries. The curve shown is for a 24 volt (12 cell) battery charger, but the curve is similar at other voltages. The timing of the phase-switching depends on the size of the battery you are using. At point #1 the battery is tested. If the battery is bad a rejuvenation algorithm is started. If the battery is good the charger goes into constant current mode until the voltage reaches 2.3 volts/cell. This allows the battery to be charged at the highest current available from the charger without overloading the charger. Then at point #2 the highest safe voltage is reached and the charger goes into constant voltage mode until the current drops to about 10% of the initial value, indicating a nominally full charge. When this is detected, at point #3 the charger goes into float charging mode at about 2.3 volts /cell to complete the fill and to maintain the battery. At this voltage the battery is safe from overcharging, and also safe from sulfating, so it is also called the maintenance mode.

The exact details of current and time depend on the charger size and the battery size.

Maintenance, keeper or ‘tender’ Chargers

Any multistage charger that has a float mode can be used to maintain batteries during the ‘off-season.’ Particularly useful are the small, inexpensive switchmode chargers that consume very little excess power. or the small low-power chargers that can automatically desulfate lead acid batteries. I use these to keep my motorcycle and lawn mower charged in the winter, and my car charged in the summer.

High Power Battery Chargers

Big battery applications such as fork lifts, floats, and golf carts have traditionally used what is called rectifiers to charge their batteries because of the relatively low price for large power levels. The rectifier consists of a transformer and diode bridge array and possibly some control or readout electronics. These work well, but the voltage might not be well regulated, which is made up for by using flooded batteries where the water can be topped off. These chargers are not appropriate for sealed lead acid batteries because their water cannot be replaced. And modern switchmode technology has made it possible to make inexpensive well regulated lead acid battery chargers such as this 8000 watt 48V charger.

DC Input Battery Chargers

There are several reasons to charge sealed lead acid batteries from DC power sources. Solar panels require a special type of charger called a solar charge controller. These are able to take whatever power is available from the solar panels, condition that power and transfer it to the battery. These chargers are specially designed to deal with the uncertainty of the available input power.

In other cases you might have a 24 volt source and want to charge a 12 volt battery, charge a 24 volt wheel chair from a 12 volt source, or other combinations of DC input battery charging. These are DC/DC converters with current limiting voltage fold-back and often multi-stage charging.

DC Input Battery Charger Examples

Input Voltage Battery Voltage Link Notes 12V 6V 12V 12V Multistage charger 12V 24V 12V 24V Heavy duty 800Watt, 60 amp charger 24V 12V 24V 12V Heavy duty, industrial 24V 24V 36V 24V Input 32V, 36V, 38V 48V 12V Heavy duty 60A charger

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Charging Lithium Batteries: The Basics

When purchasing from our company, the process of charging lithium batteries becomes an everyday part of the routine, and we understand that there’s a lot of information about our products. Whether it’s about how the technology accepts a charge or best charging practices, we’re here to outline the basics. Whether it’s best charging practices about lithium batteries, to more information about how they cycle and can be charged in order to keep your battery system running efficiently, our team is here to help.

How can I charge a LiFePO4 battery?

Our team gets this question daily, and we have a blog post on charging LiFePO4 batteries that helps address that topic. There are three main ways to charge a system: solar, alternator, and shore.

Battle Born Batteries only sells accessories from brands we know to produce quality products. One such company is Victron Energy. Battle Born is a master dealer of Victron components because they are reliable and well-built. They even offer the Victron Connect phone app where you can view all the details of your Bluetooth-capable devices.

Our team also recommends components from Progressive Dynamics and Magnum. We have plenty for purchase, so check out our store if you’re looking for more power!

One component we often recommend is the Victron Energy SmartSolar MPPT charge controllers for systems equipped with solar. With Solar Charge Controllers we recommend the following settings:

We also frequently suggest Victron’s IP-65 Blue Smart Charger because it’s waterproof, Bluetooth compatible, and has a charging profile for lithium batteries and other battery chemistries. This device connects directly to the battery and is meant for single-battery charging. It’s great for those with trolling motor applications or those with battery systems connected in series.

For alternator charging, we often recommend using a DC-to-DC charger or battery-to-battery charger. The Victron Orion-TR Smart DC-DC isolated charger is an adaptive, three-stage charger with algorithms for bulk, absorption, and float options.

You also can mix battery chemistries safely with this device, such as your AGM starting battery to your lithium house bank. Aim for a range between 14.2V and 14.6V with bulk and absorption stages and for the float stage, 13.6V is best.

While lithium batteries technically don’t need to be floated, a good majority of the devices out there still have a float charge mode. The batteries naturally float at 13.6V but reaching 14.6V is ideal and needs to happen in order to engage its balancing mechanisms.

Do I have to buy a special charger for LiFePO4 batteries?

Addressing this question, our COO. Sean. highlights how a retrofit kit from Progressive Dynamics with a con verter system has lithium battery charging options. A nother charger we recommend is a Progressive Dynamics Inteli.Power 9100 because of how easy they are to incorporate and install into your system. in addition to any Victron component.

Can I Charge My L ithium B atteries Using The Alternator?

Alternator charging is a common method to recharge lithium batteries. Charging from your alternator is a great option, however, you will need some extra equipment, like a battery isolation manager (BIM).

A well-known industry tool, this component is programmed specifically to run with our batteries. It helps with simultaneously monitoring the house and starter bank and has high internal resistance. It can certainly take more power from the alternator when compared to lead-acid batteries.

The BIM provides an extra layer of safety to make sure you don’t damage your system of three or more lithium batteries when charging from the alternator during a long drive. If you have less than three of our batteries in your system, a BIM isn’t exactly required, and instead, you can use a standard isolator. They can regulate the current up to 220 amps and prevent damaging the alternator during a long drive.

Sterling Alternator Protection devices (APD) are also available in our store to prevent damage from surges. These devices turn on with a small resistive load of milli-amp hours to reduce a possible increase in voltage due to cables breaking or any other issues. If the increase is excessively rough, it can lead to serious APD damage, but your alternator, batteries, and regulators have been protected.

The Lithium Battery Charging C ycle : to float or not to float?

Our lithium batteries don’t need to be float-charged.

When it comes to the charging cycle and our batteries, they do not need to float. When you ’re charging lithium batteries up fully. you can disconnect your charger and leave them in storage. Please note that batteries will lose a bit of charge over time, but it won’t damage the battery. They might need to be topped off when bringing them out of storage. There is no need to trickle charge your Battle Born Batteries.

However, if you have an RV with a battery bank plugged into shore, you should avoid runnin g your appliances off the battery bank. Unless you are utilizing a cutoff switch in your system, you do not have a choice to where the 12v comes from. Our team recommends that if you have a fixed voltage output converter, it’s best to use a disconnect switch to remove the batteries from the circuit and allow them to rest.

If you have a multistage charger or converter, you are able to keep the batteries in the circuit because they will be able to rest at an acceptable voltage in the final stage of the charge.

When charging a lead – acid battery, the three main stages are bulk, absorption, and float. Occasionally. there are equalization and maintenance stages for lead – acid batteries as well. This differs significantly from charging lithium batteries and their constant current stage and constant voltage stage. In the constant current stage, it will keep it steady while the battery takes the bulk of its charge. Once the maximum voltage is reached then the charger will hold that voltage and the current will begin to drop as the battery is topped off.

For a lead – acid battery. that constant voltage stage is typically called absorption, and because the lead-acid has a higher resistance. the charger will hit the higher absorption stage halfway through the charg ing cycle. You could be bulk charging at the maximum current for a couple of hours and then you’d have to wait another 2-3 hours in absorption while the battery is being topped off. By contrast, our batteries will stay in the constant current or bu lk stage for almost the entire charge cycle.

Once it hits the maximum voltage, 14.4V, then the battery is basically charged. Now we request that you hold that voltage for 15-20 minutes per battery. It’s not necessarily for the battery to get topped off but it helps the battery balance. Cell voltage starts to separate at maximum voltage. Once that voltage separation happens, we can tell wh ich cell is more charged than the others.

Once we know that, then the battery management system ( BMS ) can initiate a balancing cycle where the highest charged batteries are bled through a resistor, and then all of them can come back down to the same state of charge. Although there is no required absorption for our battery, we use the absorption stage in conventional chargers to balance the cells.

All About Multi-bank Charging:

Multi-bank charging is a great way to balance series-connected battery systems. Connected positive – to – negative to create a 24 V system, it’s important to make sure that the batteries are kept in balance. T he first battery to deplete will enter low voltage disconnect mode. triggering the other battery as well. You’ll end up with a lower capacity system than you think.

This also applies when your system experiences high voltage disconnects, so taking the se steps will protect your system in either of these extreme situations. If you keep them charged up frequently, they will be more likely to stay in balance because the BMS will internal ly balanc e the system. With this multibank charger, output leads are isolated electrically and are still able to connect each individual lead to each battery without disrupting the charge. They will both be ready for discharge and at a full state of charge.

If you want to purchase a multi-bank charger of your own, we suggest the Dual Pro Professional Series Battery charger for your system. It’s also a popular choice among the bass fishing community. It has a specific algorithm for our batteries and is offered in 2 or 4 output options.

What are the proper charging voltages for the 12V, 24V, and 48V lithium batteries?

Our Battle Born Battery charging parameters consist of the following:

charging, lithium, batteries, basics
  • Bulk/absorb = 14.2 V – 14.6 V.
  • Float = 13.6V or lower.
  • No equalization (or set it to 14.4V if possible).
  • No temperature compensation.
  • Absorption time is approximately 20 minutes per battery. if possible.

For a 12 V system, we really want to emphasize reaching 14.2 V – 14.6 V for bu lk and absorption and float to be 13.6 V or lower.

For a 24V system. we suggest a bulk and absorption rate of 28.4 V – 29.2 V and float to 27.2 V or lower. No equalization is required, but if it’s possible we suggest 28.8 V. No temperature compensation is required either, and absorption time is approximately 20 minutes per battery if that is an option.

For a 48 V system, we recommend a bulk and absorption rate of 57.4V and floating it at 56.5 V to 57 V. Sometimes. one of the batteries may trigger a high voltage disconnect in your system. The battery’s internal BMS will help handle a high voltage disconnect. Our team wants to emphasize that. overall, there’s no harm in playing aro und with charge rates to optimize your system.

How long does it take to charg e lithium batteries ?

One of our most frequently asked questions is “how long does it take to charge lithium batteries?”

Our experts note charging time depends on the specific charger in your system. Lithium-ion batteries have low internal resistance. so they will take all the current delivered from the current charge cycle. For example, if you have a 50-amp charger and a single 100-amp hour battery, d ivide the 100 amps by 50 amps to come up with a 2- hour charging time.

Another example is i f you had five 100 Ah ( amp-hour ) batteries for a total of 500 Ah and a 100-amp charger. It would take about 5 hours of charging from empty to 100 percent while factoring in enough time to balance the charg ing cycle. We don’t recommend you exceed this charge rate as it can lead to a shortened battery cycle life. In an emergency. the battery can be charged at a quicker rate if needed. but we don’t recommend you make a habit of emergency charging your battery.

If you have any additional questions on charging lithium batteries. our YouTube channel and frequently asked questions section on our website offers a wealth of information. Need more help? Please direct your questions to our sales and tech team by giving them a call at 855-292-2831 or send ing an email to [email protected].

Deep Cycle Battery FAQ

The links below are on this page. you can also just scroll down if you want to read them all.

This entire page is copyright 1998-2014 by Northern Arizona Wind Sun. Please do not use without prior permission.

  • What is a Battery?
  • Types of Batteries
  • Battery Lifespan
  • Starting, Marine, or Deep Cycle?
  • Deep Cycle Battery as a Starting Battery?
  • What Batteries are made of
  • Industrial Deep Cycle Batteries (forklift type)
  • Sealed Batteries
  • Battery Size Codes
  • Gel Cells (Gelled Electrolyte) (and why we don’t like them)
  • AGM Batteries (and why we do like them)
  • Temperature Effects
  • Cycles vs Lifespan
  • Amp-Hours. what are they?
  • Battery Voltages
  • Battery Charging (Here is where we get into the real meat)
  • Charge Controllers (for wind/solar)
  • Mini Factoids. Some small facts about batteries

The subject of batteries could take up many pages. All we have room for here is a basic overview of batteries commonly used in photovoltaic power systems. These are nearly all various variations of Lead-Acid batteries. For a very brief discussion on the advantages and disadvantages of these and other types of batteries, such as NiCad, NiFe (Nickel-Iron), etc. go to our Batteries for Deep Cycle Applications page. These are sometimes referred to as deep discharge or deep cell batteries. The correct term is deep cycle.

A printable version of this page will be available in Adobe PDF format when we finish updating this page for downloading and printing: Most of the charts have small images for faster downloading. To see the full size picture, just click on the small one.

What is a Battery?

A battery is an electrical storage device. Batteries do not make electricity, they store it, just as a water tank stores water for future use. As chemicals in the battery change, electrical energy is stored or released. In rechargeable batteries, this process can be repeated many times. Batteries are not 100% efficient. some energy is lost as heat and chemical reactions when charging and discharging. If you use 1000 watts from a battery, it might take 1050 or 1250 watts or more to fully recharge it.

Internal Resistance

Part. or most. of the loss in charging and discharging batteries is due to internal resistance. This is converted to heat, which is why batteries get warm when being charged up. The lower the internal resistance, the better. There is a good explanation and demonstration of Internal Resistance here.

Slower charging and discharging rates are more efficient. A battery rated at 180 amp-hours over 6 hours might be rated at 220 AH at the 20-hour rate, and 260 AH at the 48-hour rate. Much of this loss of efficiency is due to higher internal resistance at higher amperage rates. internal resistance is not a constant. kind of like the more you push, the more it pushes back.

Typical efficiency in a lead-acid battery is 85-95%, in alkaline and NiCad battery it is about 65%. True deep cycle AGM’s (such as Concorde) can approach 98% under optimum conditions, but those conditions are seldom found so you should figure as a general rule about a 10% to 20% total power loss when sizing batteries and battery banks.

Practically all batteries used in PV and all but the smallest backup systems are Lead-Acid type batteries. Even after over a century of use, they still offer the best price to power ratio. A few systems use NiCad, but we do not recommend them except in cases where extremely cold temperatures (-50 F or less) are common. They are expensive to buy and very expensive to dispose of due to the hazardous nature of Cadmium.

We have had almost no direct experience with the NiFe (alkaline) batteries, but from what we have learned from others we do not not recommend them. One major disadvantage is that there is a large voltage difference between the fully charged and discharged state. Another problem is that they are very inefficient. you lose anywhere from 30 to 40% in heat just by charging and discharging them. Many inverters and charge controls have a hard time with them. It appears that the only current source for new cells seems to be from Hungary. In the past they were often used by railroads as backup power, but nearly all have now changed over to newer types.

An important fact is that ALL of the batteries commonly used in deep cycle applications are Lead-Acid. This includes the standard flooded batteries, gelled, and sealed AGM. They all use the same chemistry, although the actual construction of the plates, etc varies.

NiCads, Nickel-Iron, and other types are found in a few systems, but are not common due to their expense, environmental hazards, and/or poor efficiency.

Types of Batteries

Batteries are divided in two ways, by application (what they are used for) and construction (how they are built). The major applications are automotive, marine, and deep-cycle. Deep-cycle includes solar electric (PV), backup power, traction, and RV and boat house batteries. The major construction types are flooded (wet), gelled, and sealed AGM (Absorbed Glass Mat). AGM batteries are also sometimes called starved electrolyte or drybecause the fiberglass mat is only 95% saturated with Sulfuric acid and there is no excess liquid.

Flooded may be standard, with removable caps, or the so-called maintenance free (that means they are designed to die one week after the warranty runs out). All AGM gelled are sealed and are valve regulated, which means that a tiny valve keeps a slight positive pressure. Nearly all sealed batteries are valve regulated (commonly referred to as VRLA. Valve Regulated Lead-Acid). Most valve regulated are under some pressure. 1 to 4 psi at sea level.

Battery Lifespan

The lifespan of a deep cycle battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. It can vary to extremes. we have seen L-16’s killed in less than a year by severe overcharging and water loss, and we have a large set of surplus telephone batteries that see only occasional (10-15 times per year) heavy service that was just replaced after 35 years. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage or warehouse without being charged. Even the so-called dry charged (where you add acid when you need them) have a shelf life of 18 months at most. (They are not totally dry. they are actually filled with acid, the plates formed and charged, then the acid is dumped out).

These are some typical (minimum-maximum) expectations for batteries if used in deep cycle service. There are so many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. that it is almost impossible to give a fixed number.

  • Starting: 3-12 months
  • Marine: 1-6 years
  • Golf cart: 2-7 years
  • AGM deep cycle: 4-8 years
  • Gelled deep cycle: 2-5 years
  • Deep cycle (L-16 type etc): 4-8 years
  • Rolls-Surrette premium deep cycle: 7-15 years
  • Industrial deep cycle (Crown and Rolls 4KS series): 10-20 years.
  • Telephone (float): 2-20 years. These are usually special purpose float service, but often appear on the surplus market as deep cycle. They can vary considerably, depending on age, usage, care, and type.
  • NiFe (alkaline): 5-35 years
  • NiCad: 1-20 years

Starting, Marine, or Deep-Cycle Batteries

Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead sponge, similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).

Deep cycle batteries are designed to be discharged down as much as 80% time after time and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates. not sponge. This gives less surface area, thus less instant power like starting batteries need. Although these can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge. Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The golf cart battery is quite popular for small systems and RV’s. The problem is that golf cart refers to a size of battery case (commonly called GC-2, or T-105), not the type of construction. so the quality and construction of a golf cart battery can vary considerably. ranging from the cheap off brand with thin plates up to true deep cycle brands, such as Crown, Deka, Trojan, etc. In general, you get what you pay for.

charging, lithium, batteries, basics

Marine batteriess are usually a hybrid, and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette and Concorde, for example) are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a marine battery, but most are a hybrid. Starting batteries are usually rated at CCA, or cold cranking amps, or MCA, Marine cranking amps. the same as CA. Any battery with the capacity shown in CA or MCA may or may not be a true deep-cycle battery. It is sometimes hard to tell, as the term deep cycle is often overused. we have even seen the term deep cycle used in automotive starting battery advertising. CA and MCA ratings are at 32 degrees F, while CCA is at zero degrees F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open. not much of an option.

Deep Cycle Battery as a Starting Battery

There is generally no problem with this, providing that allowance is made for the lower cranking amps compared to a similar size starting battery. As a general rule, if you are going to use a true deep cycle battery (such as the Concorde SunXtender) also as a starting battery, it should be oversized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps. That is about the same as replacing a group 24 with a group 31. With modern engines with fuel injection and electronic ignition, it generally takes much less battery power to crank and start them, so raw cranking amps is less important than it used to be. On the other hand, many cars, boats, and RV’s are more heavily loaded with power sucking appliances, such as megawatt stereo systems etc. that are more suited for deep cycle batteries. We have used the Concorde SunXtender AGM batteries in some of our vehicles with no problems.

It will not hurt a deep cycle battery to be used as a starting battery, but for the same size battery they cannot supply as much cranking amps as a regular starting battery and is usually much more expensive.

What Batteries Are Made Of

Nearly all large rechargeable batteries in common use are Lead-Acid type. (There are some NiCads in use, but for most purposes the very high initial expense, and the high expense of disposal, does not justify them). A few Lithium-Ion types are starting to make their appearance, but are much more expensive than Lead-Acid and most charge controllers do not have the correct setpoints for proper charging.

The acid is typically 30% Sulfuric acid and 70% water at full charge. NiFe (Nickel-Iron) batteries are also available. these have a very long life, but rather poor efficiency (60-70%) and the voltages are different, making it more difficult to match up with standard 12v/24/48v systems and inverters. The biggest problem with NiFe batteries is that you may have to put in 100 watts to get 70 watts of charge. they are much less efficient than Lead-Acid. What you save on batteries you will have to make up for by buying a larger solar panel system. NiCads are also inefficient. typically around 65%. and very expensive. However, NiCads can be frozen without damage, so are sometimes used in areas where the temperatures may fall below.50 degrees F. Most AGM batteries will also survive freezing with no problems, even though the output when frozen will be little or nothing.

Industrial Deep Cycle Batteries

Sometimes called fork lift, traction or stationary batteries, are used where power is needed over a longer period of time, and are designed to be deep cycled, or discharged down as low as 20% of full charge (80% DOD, or Depth of Discharge). These are often called traction batteries because of their widespread use in forklifts, golf carts, and floor sweepers (from which we get the GC and FS series of battery sizes). Deep cycle batteries have much thicker plates than automotive batteries. They are sometimes used in larger PV systems because you can get a lot of storage in a single (very large and heavy) battery.

charging, lithium, batteries, basics

Plate Thickness

charging, lithium, batteries, basics

Plate thickness (of the Positive plate) matters because of a factor called positive grid corrosion. This ranks among the top 3 reasons for battery failure. The positive plate is what gets eaten away gradually over time, so eventually there is nothing left. it all falls to the bottom as sediment. Thicker plates are directly related to longer life, so other things being equal, the battery with the thickest plates will last the longest. The negative plate in batteries expands somewhat during discharge, which is why nearly all batteries have separators, such as glass mat or paper, that can be compressed.

Automotive batteries typically have plates about.040 (4/100) thick, while forklift batteries may have plates more than 1/4 (.265 for example in larger Rolls-Surrette) thick. almost 7 times as thick as auto batteries. The typical golf cart will have plates that are around.07 to.11 thick. The Concorde AGM’s are.115, The Rolls-Surrette L-16 type (CH460) is.150, and the US Battery and Trojan L-16 types are.090. The Crown L-16HC size has.22 thick plates. While plate thickness is not the only factor in how many deep cycles a battery can take before it dies, it is the most important one.

Most industrial (fork lift) deep-cycle batteries use Lead-Antimony plates rather than the Lead-Calcium used in AGM or gelled deep-cycle batteries and in automotive starting batteries. The Antimony increases plate life and strength, but increases gassing and water loss. This is why most industrial batteries have to be checked often for water level if you do not have Hydrocaps. The self discharge of batteries with Lead-Antimony plates can be high. as much as 1% per day on an older battery. A new AGM typically self-discharges at about 1-2% per month, while an old one may be as much as 2% per week.

Sealed Batteries

Sealed batteries are made with vents that (usually) cannot be removed. The so-called Maintenance Free batteries are also sealed, but are not usually leak proof. Sealed batteries are not totally sealed, as they must allow gas to vent during charging. If overcharged too many times, some of these batteries can lose enough water that they will die before their time. Most smaller deep cycle batteries (including AGM) use Lead-Calcium plates for increased life, while most industrial and forklift batteries use Lead-Antimony for greater plate strength to withstand shock and vibration.

Lead-Antimony (such as forklift and floor scrubber) batteries have a much higher self-discharge rate (2-10% per week) than Lead or Lead-Calcium (1-5% per month), but the Antimony improves the mechanical strength of the plates, which is an important factor in electric vehicles. They are generally used where they are under constant or very frequent charge/discharge cycles, such as fork lifts and floor sweepers. The Antimony increases plate life at the expense of higher self discharge. If left for long periods unused, these should be trickle charged to avoid damage from sulfation. but this applies to ANY battery.

As in all things, there are trade offs. The Lead-Antimony types have a very long lifespan, but higher self discharge rates.

Battery Size Codes

Batteries come in all different sizes. Many have group sizes, which is based upon the physical size and terminal placement. It is NOT a measure of battery capacity. Typical BCI codes are group U1, 24, 27, and 31. Industrial batteries are usually designated by a part number such as FS for floor sweeper, or GC for golf cart. Many batteries follow no particular code, and are just manufacturers part numbers. Other standard size codes are 4D 8D, large industrial batteries, commonly used in solar electric systems.

Some common battery size codes used are: (ratings are approximate)

U1 34 to 40 Amp hours 12 volts
Group 24 70-85 Amp hours 12 volts
Group 27 85-105 Amp hours 12 volts
Group 31 95-125 Amp hours 12 volts
4-D 180-215 Amp hours 12 volts
8-D 225-255 Amp hours 12 volts
Golf Cart T-105 180 to 225 Amp hours 6 volts
L-16, L16HC etc. 340 to 415 Amp hours 6 volts

Gelled Electrolyte

Gelled batteries, or Gel Cells contain acid that has been gelled by the addition of Silica Gel, turning the acid into a solid mass that looks like gooey Jell-O. The advantage of these batteries is that it is impossible to spill acid even if they are broken. However, there are several disadvantages. One is that they must be charged at a slower rate (C/20) to prevent excess gas from damaging the cells. They cannot be fast charged on a conventional automotive charger or they may be permanently damaged. This is not usually a problem with solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to the manufacturers specifications. Most better inverters commonly used in solar electric systems can be set to limit charging current to the batteries.

Some other disadvantages of gel cells is that they must be charged at a lower voltage (2/10th’s less) than flooded or AGM batteries. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity. In hot climates, water loss can be enough over 2-4 years to cause premature battery death. It is for this and other reasons that we no longer sell any of the gelled cells except for replacement use. The newer AGM (absorbed glass mat) batteries have all the advantages (and then some) of gelled, with none of the disadvantages.

AGM (Absorbed Glass Mat) Batteries

A newer type of sealed battery uses Absorbed Glass Mats, or AGM between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. We sell the Concorde (and Lifeline, made by Concorde) AGM batteries. These are also called starved electrolyte, as the mat is about 95% saturated rather than fully soaked. That also means that they will not leak acid even if broken.

AGM batteries have several advantages over both gelled and flooded, at about the same cost as gelled:

Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage.

Nearly all AGM batteries are recombinant. what that means is that the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99% efficient, so almost no water is lost.

The charging voltages are the same as for any standard battery. no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. The Concorde (and most AGM) batteries have no charge or discharge current limits.

AGM’s have a very low self-discharge. from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. The Concorde batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged.

AGM’s do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM’s are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.

Even with all the advantages listed above, there is still a place for the standard flooded deep cycle battery. AGM’s will cost about 1.5 to 2 times as much as flooded batteries of the same capacity. In many installations, where the batteries are set in an area where you don’t have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice. AGM batteries main advantages are no maintenance, completely sealed against fumes, Hydrogen, or leakage, non-spilling even if they are broken, and can survive most freezes. Not everyone needs these features.

Temperature Effects on Batteries

Battery capacity (how many amp-hours it can hold) is reduced as temperature goes down, and increased as temperature goes up. This is why your car battery dies on a cold winter morning, even though it worked fine the previous afternoon. If your batteries spend part of the year shivering in the cold, the reduced capacity has to be taken into account when sizing the system batteries. The standard rating for batteries is at room temperature. 25 degrees C (about 77 F). At approximately.22 degrees F (-27 C), battery AH capacity drops to 50%. At freezing, capacity is reduced by 20%. Capacity is increased at higher temperatures. at 122 degrees F, battery capacity would be about 12% higher.

Battery charging voltage also changes with temperature. It will vary from about 2.74 volts per cell (16.4 volts) at.40 C to 2.3 volts per cell (13.8 volts) at 50 C. This is why you should have temperature compensation on your charger or charge control if your batteries are outside and/or subject to wide temperature variations. Some charge controls have temperature compensation built in (such as Morningstar). this works fine if the controller is subject to the same temperatures as the batteries. However, if your batteries are outside, and the controller is inside, it does not work that well. Adding another complication is that large battery banks make up a large thermal mass.

Thermal mass means that because they have so much mass, they will change internal temperature much slower than the surrounding air temperature. A large insulated battery bank may vary as little as 10 degrees over 24 hours internally, even though the air temperature varies from 20 to 70 degrees. For this reason, external (add-on) temperature sensors should be attached to one of the POSITIVE plate terminals, and bundled up a little with some type of insulation on the terminal. The sensor will then read very close to the actual internal battery temperature.

Even though battery capacity at high temperatures is higher, battery life is shortened. Battery capacity is reduced by 50% at.22 degrees F. but battery LIFE increases by about 60%. Battery life is reduced at higher temperatures. for every 15 degrees F over 77, battery life is cut in half. This holds true for ANY type of Lead-Acid battery, whether sealed, gelled, AGM, industrial or whatever. This is actually not as bad as it seems, as the battery will tend to average out the good and bad times. Click on the small graph to see a full size chart of temperature vs capacity.

One last note on temperatures. in some places that have extremely cold or hot conditions, batteries may be sold locally that are NOT standard electrolyte (acid) strengths. The electrolyte may be stronger (for cold) or weaker (for very hot) climates. In such cases, the specific gravity and the voltages may vary from what we show.

Cycles vs Lifespan

A battery cycle is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. However, there are often ratings for other depth of discharge cycles, the most common ones are 10%, 20%, and 50%. You have to be careful when looking at ratings that list how many cycles a battery is rated for unless it also states how far down it is being discharged. For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. If you look at the fine print, it has that rating only at 5% DOD. it is much less when used in an application where they are cycled deeper on a regular basis. Those same batteries are rated at less than 5 years if cycled to 50%. For example, most golf cart batteries are rated for about 550 cycles to 50% discharge. which equates to about 2 years.

Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. Obviously, there are some practical limitations on this. you don’t usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It’s just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor. Also, there is an upper limit. a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film. The graph above shows how lifespan is affected by depth of discharge. The chart is for a Concorde Lifeline battery, but all lead-acid batteries will be similar in the shape of the curve, although the number of cycles will vary.

Battery Voltages

All Lead-Acid batteries supply about 2.14 volts per cell (12.6 to 12.8 for a 12 volt battery) when fully charged. Batteries that are stored for long periods will eventually lose all their charge. This leakage or self discharge varies considerably with battery type, age, temperature. It can range from about 1% to 15% per month. Generally, new AGM batteries have the lowest, and old industrial (Lead-Antimony plates) are the highest. In systems that are continually connected to some type charging source, whether it is solar, wind, or an AC powered charger this is seldom a problem. However, one of the biggest killers of batteries is sitting stored in a partly discharged state for a few months. A float trickle charge should be maintained on the batteries even if they are not used (or, especially if they are not used). Even most dry charged batteries (those sold without electrolyte so they can be shipped more easily, with acid added later) will deteriorate over time. Max storage life on those is about 18 to 30 months.

Batteries self-discharge faster at higher temperatures. Lifespan can also be seriously reduced at higher temperatures. most manufacturers state this as a 50% loss in life for every 15 degrees F over a 77 degree cell temperature. Lifespan is increased at the same rate if below 77 degrees, but capacity is reduced. This tends to even out in most systems. they will spend part of their life at higher temperatures, and part at lower. Typical self discharge rates for flooded are 5% to 15% per month.

Myth: The old myth about not storing batteries on concrete floors is just that. a myth. This story has been around for 100 years, and originated back when battery cases were made up of wood and asphalt. The acid would leak from them, and form a slow-discharging circuit through the now acid-soaked and conductive floor.

State of Charge

State of charge, or conversely, the depth of discharge (DOD) can be determined by measuring the voltage and/or the specific gravity of the acid with a hydrometer. This will NOT tell you how good (capacity in AH) the battery condition is. only a sustained load test can do that. Voltage on a fully charged battery will read 2.12 to 2.15 volts per cell, or 12.7 volts for a 12 volt battery. At 50% the reading will be 2.03 VPC (Volts Per Cell), and at 0% will be 1.75 VPC or less. Specific gravity will be about 1.265 for a fully charged cell, and 1.13 or less for a totally discharged cell. This can vary with battery types and brands somewhat. when you buy new batteries you should charge them up and let them sit for a while, then take a reference measurement. Many batteries are sealed, and hydrometer reading cannot be taken, so you must rely on voltage. Hydrometer readings may not tell the whole story, as it takes a while for the acid to get mixed up in wet cells. If measured right after charging, you might see 1.27 at the top of the cell, even though it is much less at the bottom. This does not apply to gelled or AGM batteries.

False Capacity

A battery can meet the voltage tests for being at full charge, yet be much lower than it’s original capacity. If plates are damaged, sulfated, or partially gone from long use, the battery may give the appearance of being fully charged, but in reality acts like a battery of much smaller size. This same thing can occur in gelled cells if they are overcharged and gaps or bubbles occur in the gel. What is left of the plates may be fully functional, but with only 20% of the plates left. Batteries usually go bad for other reasons before reaching this point, but it is something to be aware of if your batteries seem to test OK but lack capacity and go dead very quickly under load.

On the table below, you have to be careful that you are not just measuring the surface charge. To properly check the voltages, the battery should sit at rest for a few hours, or you should put a small load on it, such as a small automotive bulb, for a few minutes. The voltages below apply to ALL Lead-Acid batteries, except gelled. For gel cells, subtract.2 volts. Note that the voltages when actually charging will be quite different, so do not use these numbers for a battery that is under charge.

Amp-Hours. What Are They?

All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x.333 (hours), or 6.67 AH. The generally accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the 20 hour rate. (Some, such as the Concorde AGM, use the 24 hour rate, which is probably a better real-world rating). This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as that is a typical daily duty cycle. Sometimes the 100 hour rate is given just to make the battery look better than it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements.

Why amp-hours are specified at a particular rate:

Because of something called the Peukert Effect. The Peukert value is directly related to the internal resistance of the battery. The higher the internal resistance, the higher the losses while charging and discharging, especially at higher currents. This means that the faster a battery is used (discharged), the LOWER the AH capacity. Conversely, if it is drained slower, the AH capacity is higher. This is important because some manufacturers and vendors have chosen to rate their batteries at the 100 hour rate. which makes them look a lot better than they really are. Here are some typical battery capacities from the manufacturers data sheets:

Battery Type 100 hour rate 20 hour rate 8
Trojan T-105 250 AH 225 AH n/a
US Battery 2200 n/a 225 AH 181 AH
Concorde PVX-6220 255 AH 221 AH 183 AH
Surrette S-460 (L-16) 429 AH 344 AH 282 AH
Trojan L-16 400 AH 360 AH n/a
Surrette CS-25-PS 974 AH 779 AH 639 AH

Here are no-load typical voltages vs state of charge

(figured at 10.5 volts = fully discharged, and 77 degrees F). Voltages are for a 12 volt battery system. For 24 volt systems multiply by 2, for 48 volt system, multiply by 4. VPC is the volts per individual cell. if you measure more than a.2 volt difference between each cell, you need to equalize, or your batteries are going bad, or they may be sulfated. These voltages are for batteries that have been at rest for 3 hours or more. Batteries that are being charged will be higher. the voltages while under charge will not tell you anything, you have to let the battery sit for a while. For longest life, batteries should stay in the green zone. Occasional dips into the yellow are not harmful, but continual discharges to those levels will shorten battery life considerably. It is important to realize that voltage measurements are only approximate. The best determination is to measure the specific gravity, but in many batteries this is difficult or impossible. Note the large voltage drop in the last 10%.

State of Charge 12 Volt battery Volts per Cell
100% 12.7 2.12
90% 12.5 2.08

Why 10.5 Volts?

Throughout this FAQ, we have stated that a battery is considered dead at 10.5 volts. The answer is related to the internal chemistry of batteries. at around 10.5 volts, the specific gravity of the acid in the battery gets so low that there is very little left that can do. In a dead battery, the specific gravity can fall below 1.1. Some actual testing was done recently on a battery by one of our solar forum posters, and these are his results:

I just tested a 225 ahr deep cycle battery that is in good working order. I put a load on it 30a for 4 hrs it dropped its voltage to 11.2 I then let it cool down for 2 hrs

then put the load back on again in 1hr 42 mins it dropped to 10.3v 35 mins under 30a load 9.1v (273w) 10 mins later max output current 11.6a 8.5v (98.6w) 5 mins later max output current 5.2 amps 7.9v (41w) 3 mins later 7.6v and 2.3a (17.5w)

This shows after it gets below 10.3 v you only have 35 mins of anything useful available from the battery.

battery is now dead and most likely will not fully recover

Battery Charging

Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.

Bulk Charge. The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no correct voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.

Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts. (The internal resistance gradually goes up because there is less and less to be converted back to normal full charge).

Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it’s main purpose is to keep an already charged battery from discharging. PWM, or pulse width modulation accomplishes the same thing. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called pulse width because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.

Chargers: Most garage and consumer (automotive) type battery chargers are bulk charge only, and have little (if any) voltage regulation. They are fine for a quick boost to low batteries, but not to leave on for long periods. Among the regulated chargers, there are the voltage regulated ones, such as Iota Engineering, PowerMax, and others, which keep a constant regulated voltage on the batteries. If these are set to the correct voltages for your batteries, they will keep the batteries charged without damage. These are sometimes called taper charge. as if that is a selling point. What taper charge really means is that as the battery gets charged up, the voltage goes up, so the amps out of the charger goes down. They charge OK, but a charger rated at 20 amps may only be supplying 5 amps when the batteries are 80% charged. To get around this, Xantrex (and maybe others?) have come out with Smart, or multi-stage chargers. These use a variable voltage to keep the charging amps much more constant for faster charging.

We stock all of the Iota Engineering battery chargers.

Charge Controllers

A charge controller is a regulator that goes between the solar panels and the batteries. Regulators for solar systems are designed to keep the batteries charged at peak without overcharging. Meters for Amps (from the panels) and battery Volts are optional with most types. Some of the various brands and models that we use and recommend are listed below. Note that a couple of them are listed as power trackers. for a full explanation of this, see our page on Why 130 watts does not equal 130 watts.

Most of the modern controllers have automatic or manual equalization built in, and many have a LOAD output. There is no best controller for all applications. some systems may need the bells and whistles of the more expensive controls, others may not.

These are some of the charge controllers that we recommend, but almost any modern controller will work fine. Exact model will depend on application and system size, amperage and voltage.

Xantrex Morningstar Midnite Solar Outback Power Steca You can find all these brands, as well as others, in our charge controller section.

Using any of these will almost always give better battery life and charge than on-off or simple shunt type regulators

Battery Charging Voltages and Currents:

Most flooded batteries should be charged at no more than the C/8 rate for any sustained period. While some battery manufacturers state a higher maximum charge rate, such as C/3, higher charge rates can result in high battery temperatures and/or excessive bubbling and loss of liquid. (C/8 is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps.) Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. Concorde and some other AGM batteries are a special case. they can be charged at up the the Cx4 rate, or 400% of the capacity for the bulk charge cycle for a short period. However, since very few battery cables can take that much current, we don’t recommend you try this at home. To avoid cable overheating, you should stick to C/4 or less.

Charging at 15.5 volts will give you a 100% charge on Lead-Acid batteries. Once the charging voltage reaches 2.583 volts per cell, charging should stop or be reduced to a trickle charge. Note that flooded batteries MUST bubble (gas) somewhat to ensure a full charge, and to mix the electrolyte. Float voltage for Lead-Acid batteries should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12 volt battery. At higher temperatures (over 85 degrees F) this should be reduced to about 2.10 volts per cell.

Never add acid to a battery except to replace spilled liquid. Distilled or deionized water should be used to top off non-sealed batteries. Float and charging voltages for gelled batteries are usually about 2/10th volt less than for flooded to reduce water loss. Note that many shunt-type charge controllers sold for solar systems will NOT give you a full charge. check the specifications first. To get a full charge, you must continue to apply a current after the battery voltage reaches the cutoff point of most of these types of controllers. This is why we recommend the charge controls and battery chargers listed in the sections above. Not all shunt type controllers are 100% on or off, but most are.

Flooded battery life can be extended if an equalizing charge is applied every 10 to 40 days. This is a charge that is about 10% higher than normal full charge voltage, and is applied for about 2 to 16 hours. This makes sure that all the cells are equally charged, and the gas bubbles mix the electrolyte. If the liquid in standard wet cells is not mixed, the electrolyte becomes stratified. You can have very strong solution at the bottom, and very weak at the top of the cell. With stratification, you can test a battery with a hydrometer and get readings that are quite a ways off. If you cannot equalize for some reason, you should let the battery sit for at least 24 hours and then use the hydrometer. AGM and gelled should be equalized 2-4 times a year at most. check the manufacturers recommendations, especially on gelled.

Battery Aging

As batteries age, their maintenance requirements change. This means longer charging time and/or higher finish rate (higher amperage at the end of the charge). Usually older batteries need to be watered more often. And, their capacity decreases while the self-discharge rate increases.

Mini Factoids

Nearly all batteries will not reach full capacity until cycled 10-30 times. A brand new battery will have a capacity of about 5-10% less than the rated capacity.

Batteries should be watered after charging unless the plates are exposed, then add just enough water to cover the plates. After a full charge, the water level should be even in all cells and usually 1/4 to 1/2 below the bottom of the fill well in the cell (depends on battery size and type).

In situations where multiple batteries are connected in series, parallel or series/parallel, replacement batteries should be the same size, type, and manufacturer (if possible). Age and usage level should be the same as the companion batteries. Do not put a new battery in a pack which is more than 6 months old or has more than 75 cycles. Either replace with all new or use a good used battery. For long life batteries, such as the Surrette and Crown, you can have up to a one year age difference.

The vent caps on flooded batteries should remain on the battery while charging. This prevents a lot of the water loss and splashing that may occur when they are bubbling.

When you first buy a new set of flooded (wet) batteries, you should fully charge and equalize them, and then take a hydrometer reading for future reference. Since not all batteries have exactly the same acid strength, this will give you a baseline for future readings.

When using a small solar panel to keep afloat (maintenance) charge on a battery (without using a charge controller), choose a panel that will give a maximum output of about 1/300th to 1/1000th of the amp-hour capacity. For a pair of golf cart batteries, that would be about a 1 to 5-watt panel. the smaller panel if you get 5 or more hours of sun per day, the larger one for those long cloudy winter days in the Northeast.

Lead-Acid batteries do NOT have a memory, and the rumor that they should be fully discharged to avoid this memory is totally false and will lead to early battery failure.

Inactivity can be extremely harmful to a battery. It is a VERY poor idea to buy new batteries and save them for later. Either buy them when you need them or keep them on a continual trickle charge. The best thing. if you buy them, use them.

Only clean water should be used for cleaning the outside of batteries. Solvents or spray cleaners should not be used.

Some Peukert Exponent values (not complete, just for info). We don’t have a lot of data. Trojan T-105 = 1.25; Optima 750S = 1.109; US Battery 2200 = 1.20.

information. Manufacturers Websites

Trojan Battery. not a lot of real technical info here, but has all the specifications.Rolls Battery. Specs and data on the Rolls Surrette deep cycle and marine batteriesConcorde. specs and data on all the Concorde batteries, including Lifeline.Discover Battery. Lots of info on the Discover Battery brand of batteries.Discover Solar. A solar specific site for the Discover Battery brand.SimpliPhi

How Long Will A 100W Solar Panel Take To Charge A 100Ah Battery?

How long will it take to charge a 100Ah battery with a 100W solar panel?

  • how much power can a 100Ah solar panel produce?
  • what is the irradiance (sun’s energy) level in your location?
  • what type of solar charge controller will you use?
  • which type of battery will you use, lithium based or lead-acid?
  • what is the usual Depth of Discharge for your 100Ah battery?

The biggest factor is to determine how much energy needs to put back into the battery. Everything else flows from this.

A 100W rated solar panel using an MPPT solar charge controller will take approximately 12.5 hours to fully recharge a 50% discharged 100Ah lead-acid deep-cycle battery. 200 watts of solar panels is recommended to recharge the same 100Ah battery in one day, if the battery is used for home energy storage.

How much power can a 100 watt solar panel produce?

Every solar panel comes with a label stating the electrical specifications, which can also be found on the panel’s specification PDF sheet online.

The image below shows the electrical specs. for a Centsys 100 watt panel.

The main values that interest us are the open circuit volts (Voc) 22V, Maximum Power Point voltage (Vmpp) 18 V and Maximum Power Point current (Impp) 5.56A.

The typical manufacturer’s spec sheet uses the STC (Standard Test Conditions), which are ideal test conditions.

The important thing to note is that these are ideal values under perfect laboratory test conditions.

It’s rare to find these conditions in the real world. As a general rule, expect to get only 75% of the stated power out of a standard quality 100 watt solar panel.

This mens that you should base any calculations on 75% of the stated maximum current, which for the above panel is a little over 4 amps.

Table – 100 solar panel annual energy output by irradiance per location

New York, NY

Birmingham, UK

Brisbane, AU

Irradiance (peak-sun-hours/day)

100W solar panel output per year (kWh)

100W solar panel output per day (kWh)

What are the two types of lead acid battery?

Lead-acid batteries come in two basic types – auto, for cars and trucks, and deep-cycle (leisure) for RV solar panel use. There is a hybrid battery for marine use which combines the two types.

Car batteries can deliver hundreds of amps to crank and start a cold car or truck engine. They shouldn’t be discharged regularly much more than 20% of their capacity.

How far can you drain a deep cycle battery?

On the other hand, deep-cycle lead-acid batteries can be discharged up to 80% of their capacity. However, 50% Depth of Discharge is recommended for maximum life.

As solar energy storage is essentially deep-cycle, I’ll FOCUS on this type for this article.

I own a 100Ah Varta marine battery, which I use as part of an emergency solar generator for home use.

It can run basic lights and appliances overnight if the power goes out, so it’s a useful backup power supply.

How many solar panels does it take to charge a 100ah battery?

Assuming a 100Ah solar panel current output of 4 amps minimum, then a 100Ah battery depleted 50% will need 12.5 hours to fully recharge.

If the battery was to be used as solar energy storage for use at night-time, then 200 watts of solar panels is recommended to ensure that the battery is recharged fully each day.

Lithium iron phosphate vs lead acid

Lead acid and lithium iron phosphate have different characteristics

Lithium iron phosphate batteries (LiFeP04) are more expensive than lead acid but they have advantages. They are lighter, last much longer and are inherently deep-cycle.

You don’t have to purchase a special deep-cycle battery, because deep depth of discharge characteristics are part of their chemistry.

I have a 14.4 volts 30Ah LiFeP04 model which can be discharged 95% regularly with no damage.

However, 80% discharge is recommended if you want the battery to last a long time – 2000 charge/discharge cycles for 95% discharge and a whopping 5000 cycles for 80%.

This makes a big difference to charging time, because there’s more energy to put back in the battery.

A 100W solar panel with an MPPT solar charger will take about 20 hours to fully recharge an 80% discharged 100Ah lithium iron phosphate battery. 250 watts of solar panels is recommended to fully recharge a 100Ah LiFeP04 battery in a day, if it is to be used for home energy storage.

Why do you need a solar charge controller?

Solar charge controllers come in two types – MPPT and PWM

Typical open circuit voltage for a 100 watt solar panel is about 22 volts, while it delivers maximum current at 18 volts.

If you connect the panel directly to a 12 volt battery, there is no way of knowing what the charge current will be. In fact, in the early stages of charging, there would probably be no problem.

However, eventually the battery would be full but the panel may still be pushing current into the battery resulting in permanent damage to the internal structure.

The charging voltage needs to be regulated so that the charging current is controlled throughout the charging cycle.

The difference between MPPT and PWM solar charge controllers

PWM (Pulse Width Modulation) chargers are cheap and give a much coarser control than their more expensive MPPT cousins.

They work by splitting up the charging current into pulses, which are then width-modulated to give an average voltage. The average value of this modulated voltage determines the current.

PWM chargers are not very efficient but they are really cheap. There are many brands available for less than 10.

MPPT solar charges work in a different way. The Maximum Power Point of a solar panel is when the volts and amps are at the values necessary to deliver maximum power.

An MPPT controller tracks this point, which is dynamic according to changes in irradiance and other factors – the ‘T’ stands for ‘Tracking‘.

The Maximum Power Point happens when the internal resistance of the load (battery) equals the internal resistance of the solar panel.

The MPPT controller matches the panel internal resistance so that maximum power is drawn from the panel. These controllers are up to 30% more efficient than the cheaper PWM type.

How many solar panels do I need to charge a 100Ah battery in 5 hours?

If the battery is completely discharged (and it shouldn’t be!) then it will need:

100Ah/5 = 20 amps/hour

However, solar charge controllers have an efficiency of about 90%, so we need to add 10% to this figure, making it 22 amps/hour.

A 100 watt solar panels delivers about 5 amps in full mid-day sunshine, so the solar panel can be calculated this way:

22 amps/5 amps = 4.4 solar panels of 100 watt rating

The above assumes irradiance of 1000/m2 for the 5 hours period.

5 solar panels rated at 100 watts would be needed to charge a 100Ah battery in 5 hours.

How long does it take a 100 watt solar panel to charge a battery?

For charging batteries with solar you should gather the following information:

  • What is battery capacity when fully charged?
  • Depth of discharge in regular operation
  • Irradiance in your location? (If not known, use 4 peak sun hours as an average value.)
  • The type solar controller to be used (MPPT is more efficient and reommended.)

As a general rule, a typical size 12v 50Ah auto battery at 20% discharge will need 2 hours to fully recharge with a 100 watt solar panel.

A lead-acid deep-cycle 12v 50Ah battery at 50% discharge will take about 4 hours to fully recharge using a 100 watt solar panel.

Both examples above assume a solar panel current output of 5.75 amps using an MPPT controller.

How long will a 100Ah battery run a fridge?

Fridges don’t operate in quite the same way as many home appliances.

Like freezers and air-conditioners, they use compressor motors to drive the cooling cycle, which start and stop as demanded by the device internal temperature.

When a motor starts up it pulls an inrush current which can be several times bigger than the normal running current. The motor has 3 states – not running, starting and continuous running.

A 100Ah deep-cycle lead-acid battery will power a refrigerator with energy consumption of 630kWh/annum for 13.3 hours. 80% DoD (Depth of Discharge) is assumed. At the recommended discharge of 50% a 100Ah battery can power the same fridge for 8.3 hrs. A lithium (LiFeP04) 100Ah battery will power the same fridge for 15.8 hours with 95% discharge.

How many hours will a 100Ah battery run a fridge?

How long will a 100Ah battery run an appliance that requires 1000w?

Use the table below to find 100Ah run-time with various loads:

Hours Run Time 12 volts 100Ah deep-cycle lead-acid battery (50% recommended discharge)

Load supplied in watts

Run time in hours

AC Load (inverter losses subtracted)

How to Charge Dakota Lithium and LiFePO4 Batteries

All Dakota Lithium and most lithium-ion batteries require a higher voltage than lead acid batteries to fully charge and perform best when charged with a lithium specific battery charger that charges at 14.4 – 14.8 Volts. This includes Dakota Lithium Iron Phosphate (LiFePO4) and Lithium Nickel Manganese Cobalt (NMC) batteries. A battery charger for a lead acid battery will work to partially charge a lithium battery, but only to a maximum of 60-80% of the lithium battery’s capacity. The voltage level of a full lead acid battery is about a volt lower than the voltage of a full lithium battery. As a result, the lead acid charger will think the battery is “full” once it reaches the lower voltage that is associated with a full lead acid battery. The result is lead acid battery chargers work, but only charge to 60-80% of the lithium battery’s capacity. Please note that lead acid chargers do not damage the battery, they just prevent the battery from reaching it’s full capacity and performance potential. The performance limitations of lead acid chargers being used for lithium batteries is significant enough that most lithium battery owners prefer to use lithium specific chargers. Lithium specific chargers maximize the performance and value of a lithium battery.

One exception is solar charge controllers. A solar charge controller transforms the energy produced by a solar panel to the ideal voltage to charge your battery. Solar charge controllers always perform better when they are lithium battery specific or have a lithium setting. Enough solar power is lost due to the inefficiency of a lead acid solar charge controller attached to a lithium battery that the solar panels may fail to adequately charge the battery. An example of a lithium specific solar charge controller would be the Victron SmartSolar MPPT 75/15 Solar Charge Controller. For more see the how to charge my battery from solar panels section below.

What voltage is required to charge my lithium batteries?

Dakota Lithium Iron Phosphate (LiFePO4) 12V batteries should be charged at 14.4 Volts (V). For batteries wired in series multiply 14.4V by the number of batteries. For example, a 24V battery bank requires a charger voltage of 28.8V. 36V requires 43.2V, etc.

Dakota Lithium Battery Voltage | Recommended Charging Voltage | Recommended Charging Speed (C)

How fast can I charge my battery?

Calculate the charge time by dividing the capacity of the battery (Ah for Amp Hours) by the charger output (A for Amps). For example, a 12V 100Ah Dakota Lithium battery includes a free 12V 10A LiFePO4 battery charger that charges the battery from empty to full in 10 hours (100 Ah divided by 10 A = 10 hours).

For the longest lifespan LiFePO4 batteries should be charged at less than.3C, or 3 hours or more of charging time. But all Dakota Lithium batteries can be charged at a rate of up to 1C and a charging time as low as 1 hour. For other brands confirm that max charging amps in the battery’s specifications. 0.5C (2 hours) is a common max charging speed for lithium batteries.

Dakota Lithium Battery | Recommended LiFePO4 Charger Charge Time | Faster Charger Option

Which lithium charger brand can I use for LiFePO4 batteries?

Most LiFePO4 chargers have an output of 14.6V – 14.8V which will charge Dakota Lithium batteries, and any LiFePO4 fully. Here at Dakota Lithium, we recommend using Dakota Lithium LiFePO4 chargers because they provide an optimal voltage of 14.4V, which slightly increases the battery’s lifespan by stressing the battery chemistry less during charging. Dakota Lithium LiFePO4 chargers also undergo our company’s redundant quality control process, ensuring every charger is optimized and safe to use with all our LiFePO4 batteries. Other programmable chargers can also be used if needed and should be set to output 14.4V and disconnected after charging. VRLA chargers and other lithium-ion batteries’ chargers do not output the correct voltage for charging the battery fully.

Can I charge my batteries with solar panels via a solar charger?

Yes, for smaller solar panels that are less than 4 or lithium compatible solar charge controller is strongly recommended. For system with more than 200 watts of solar energy a solar charge controller is required for efficiency and safety. A solar charge controller takes the energy from the solar panels and turns it into the optimal voltage for charging your battery. For example, if you had installed a 100-Watt Solar Panel on the roof of your van or RV you would then need a Victron SmartSolar MPPT 75/15 Solar Charge Controller or similar sized solar charge controller to take the energy from the panel that is at 18 Volts (V) and transform it into 14.4 Volts, the optimal voltage for a Dakota Lithium or any LiFePO4 battery. The solar charge controller also increases the efficiency of the transfer of energy from the solar panels to the battery, increasing charge time and overall system efficiency. Approximately 100 – 200 Watts of solar power charges 100Ah of battery capacity depending on use and on climate and latitude. For example, if you use your boat or RV mostly on weekends you need less, if living on it full time you will need more. And if you are living in Canada, you will need more solar panels then someone living in Arizona.

Here’s a size chart for what size of solar panels is needed to fully charge one lithium battery.

Size of Battery | Recommended Solar Panel Capacity | Solar Charge Controller

12V 54Ah Dakota Lithium | 100-200-Watt Rooftop Solar Panels | 15 Amp MPPT Victron or Similar

12V 100Ah Dakota Lithium | 100-200 Watt Rooftop Solar Panels | 15 Amp MPPT Victron or Similar

12V 200Ah Dakota Lithium | 200-Watt Rooftop Solar Panels | 15 Amp MPPT Victron or Similar

Can I use an onboard charger to charge lithium batteries?

Yes, Dakota Lithium and all LiFePO4 batteries can be charged with onboard chargers. Pre-assembled wiring kits for connecting your batteries to onboard chargers are available here Trolling Motor Wiring Kits. If the onboard charger has a lithium setting, or can be set to 14.4V it will fully charge the battery. Chargers that do not go as high as 14.4V, such as onboard chargers for marine AGM or lead acid batteries that do not have a lithium setting will not be able to charge the battery fully. If possible, disconnect the batteries when they are completely charged.

Can I charge a lithium battery using my car, van, or boat’s alternator?

Yes, but only lithium and LiFePO4 batteries that are designed for automotive use can be charged directly by the alternator. For automotive or marine cranking applications where you are starting an engine and charging the starter battery from the engine’s alternator, we recommend the Dakota Lithium Plus 12V 60Ah Dual Purpose 1000 CCA battery. This battery provides up to 1,000 cold cranking amps to start a vehicle’s engine and can charge up to 80 Amps from a vehicle’s alternator. For most LiFePO4 batteries on the market, including all Dakota Lithium deep cycle batteries, a DC-DC charger is required to charge a lithium battery from an engine’s alternator.

Why is a DC-DC charger needed to charge a lithium battery from a car’s alternator?

DC-DC chargers are needed in most cases when using alternators to charge batteries (exception is the Dakota Lithium Plus 12V 60Ah 1000CCA battery which is designed for use in a boat or car’s engine). Without a DC-DC charger, an alternator’s power output can charge the battery at a rate more than 1C, which causes damage to the battery and may turn the battery off by triggering the overcharging protection in Dakota Lithium’s battery management system (BMS). Also, charging a large capacity ‘house bank’ of batteries via the alternator will cause it to run at full nameplate output power, which may overheat and/or damage the alternator. For alternator charging, a DC-DC charger is recommended, or the user may carefully review and choose a “DL” model pack from our catalog and use it without a DC-DC charger in circumstances where the alternator output matches the battery charging abilities well.

Should I use float chargers or battery maintainers for my lithium battery?

No, LiFePO4 batteries should be disconnected from the charger when fully charged. Float charging, or maintainers are not good for lithium batteries. Keeping a constant float charge or topping off charge also can cause metal plating and will reduce the lifespan of lithium batteries. Dakota Lithium batteries also have a low self-discharge rate of

How do I know my charging is working?

The light on the battery charger turns green when plugged into an outlet. While charging, the light turns red. It turns green again when the battery is fully charged. The charger should be disconnected when the battery is fully charged to prevent over-charging which can cause permanent battery damage.

Why won’t my lithium battery charge? How to troubleshoot battery problems

Checking the battery and a charger with a voltmeter is a good place to start when experiencing issues. Test the battery before and after attempting a full charge, and when the battery is depleted. Also, test the output on the charger, it should measure 14.4V when working properly. Getting a voltage charge of less than 1V is evidence that the B.M.S. has been triggered on the battery to protect it from a potentially dangerous condition. The B.M.S. can usually be reset by charging the battery with a Dakota Lithium charger.

What is the battery voltage when my battery is full or depleted?

Batteries measure around 14.4V when they are fully charged and quickly drop to about 13.4V when the charger is removed. They provide consistent power between 13.4 to about 12.8V and quickly deplete to 9.7V at the end of the discharge. Dakota Lithium Iron Phosphate batteries have a flat voltage curve. This means that the voltage will be fairly steady throughout use, and only drop below a useful voltage when the battery is nearly empty. Lead acid batteries have a steep voltage drop and it is common that a lead acid battery’s voltage is no longer useable when the battery still have 60% of capacity left. This flat voltage curve is why Dakota Lithium batteries have twice the usable power even though the battery has the same amount of energy inside the battery. A 100Ah Dakota Lithium battery will last twice as long as a 100Ah AGM or lead acid battery even though the name plate or energy rating is the same. Please note: Seeing a low voltage of

What is the B.M.S.?

B.M.S. – Battery Management System – is the intelligent component of the battery which monitors and manages several aspects of its performance, including charge and discharge rates. The B.M.S. also provides safety protection in the case of short circuit, over charging, or the battery getting too hot. The B.M.S. will trigger and shut down the battery in instances when the charge/discharge current is too high, the temperature is too high, or to prevent over charging or over discharge. BMS design may vary with brand. Dakota Lithium engineers design the battery management system microchips for our batteries in house to meet specific safety standards including cold temperature charging protection, high temperature protection, cell balancing, and other features that extend the lifespan and performance of the battery. Please note: Seeing a low voltage of

How can I calculate the battery’s run time?

Calculate the battery run time by dividing the battery capacity (Ah) by the power draw of anything connected to the battery (A). For example, an electric cooler that a power draw of 1 amp can be powered for 100 hours by a Dakota Lithium or LiFePO4 battery or 40-50 hours by an AGM or lead acid battery.

What happens inside my battery when charging or discharging?

Dakota Lithium batteries transfer a charge via lithium-ions between lithium iron phosphate in the cathode and graphite in the anode using intercalation. The ions never become lithium metal and stay in the ion state, which makes the batteries rechargeable.

At what temperatures can I charge and operate my batteries?

LiFePO4 batteries can be safely discharged below freezing temperature and provide up to 70% of their power, VLRA batteries do not work at that temperature. Dakota Lithium batteries can also operate safely in temperatures up to 149°F, while VRLA batteries’ service life halves every 18°F increase in temperature over 120°F. LiFePO4 batteries can be charged in environments up to 113°F but should not be charged in direct sunlight above 90°F. Charging lithium iron phosphate batteries below 32°F not only makes your batteries unsafe, but it also will drastically and permanently reduce the capacity.

How should I store my battery? Does it self-discharge?

LiFePO4 batteries have a low self-discharge rate of 3 – 5% per month, so they can be left in a partially discharged state for over a year without damaging the battery. This is 5X less than the self-discharge rate of VRLA batteries, but it is higher than some other lithium based systems.

L.F.P. batteries should be stored well charged at a temperature between 40 – 95°F, however, they need to be above 32°F to charge. We recommend charging your lithium batteries every two months to ensure they do not completely drain.

How do I use a voltmeter?

To use a voltmeter, first, make sure it is in DC (direct current) mode and then connect the red clip to the red/ battery terminal and the black clip to the black/- battery terminal when measuring a battery’s voltage. Measure the voltage from a charger by touching the red clip to the positive contact point on the charger, and the black clip to the negative contact point.

How can I connect my batteries in series and parallel circuits?

The batteries can be connected in a string to increase the total voltage or capacity in a system, but batteries must match in all criteria including type, voltage, and amperage. Connecting two batteries in parallel combines their capacity (Ah), while connecting the batteries in series combines the batteries’ voltages. The batteries can be charged while in the system, by connecting a charger with matching voltage of the system to the positive terminal of the first battery and the negative terminal of the last battery.

How are Dakota Lithium batteries designed to work in Lead Acid battery systems?

LiFePO4 batteries are one-third the size of VRLA batteries of the same capacity, but they are designed to be “drop-in replacements” for 12V, 24V, 36V and 48V systems designed around lead-acid batteries. For example, four LiFePO4 cells in series can provide 12.8V, which can be used to replace systems made around traditional 6 2V cell batteries.

What if one battery loses charge faster in a circuit?

When batteries are connected in a series, they can become unbalanced, this can be detected by testing each battery with a voltmeter. Separately charging each battery can fix this issue.

Safety information:

Do not charge any damaged batteries.

Do not short circuit lithium batteries.

Do not exceed the max discharge specifications of the battery (for example, if the battery has a max discharge of 10 amps do not try to run a trolling motor off of it that pulls 20 amps)

Do not puncture the outer case or disassemble the battery

Batteries over 300Wh are subject to hazmat regulations when shipping.

When shipping a battery plenty of anti static bubble wrap should be used to protect it from blunt damage. The terminal posts should be removed, if possible, to prevent accidental shorting.

Safety: How Safe are Lithium Iron Phosphate Batteries?

We have all heard and read past accounts of lithium batteries exploding or catching fire when compromised during trauma or over charging. But with the development of new chemistries and advanced manufacturing techniques, lithium ion technology is now one of the most popular battery options available. A common misunderstanding is that all lithium ion batteries are the same. There are different chemistries available that provide various advantages and disadvantages. Another factor in safety is the manufacturing of the battery and the technology of the battery including battery management systems (BMS) to monitor the battery’s performance.

BATTERY MANAGEMENT SYSTEM (BMS) – Ensures safety and long battery lifespan

All Dakota Lithium batteries include an active BMS protection circuit that handles cell balancing, low voltage cutoff, high voltage cutoff, short circuit protection and temperature protection for increased performance and longer life. Safety measures provided by the BMS prevent overheating. All Dakota Lithium batteries have a BMS that can support linking batteries in series or parallel.


Different Li-ion batteries use different chemistries. Dakota Lithium exclusively engineers our batteries using lithium iron phosphate or LiFePO4 for short. Lithium Iron Phosphate batteries are the safest lithium battery chemistry. Unlike the cell phone battery in your. or the laptop battery on your desk, the structural stability of LiFePO4 results in significantly less heat generation compared to

other lithium chemistries.

NO THERMAL RUNAWAY – Dakota Lithium cells do not produce oxygen

The main cause of fire or explosion of a lithium ion battery is due to the cells being compromised or ruptured, which causes thermal runaway. Without proper management, thermal runaway may result in fire. Dakota LiFePO4 is extremely stable and does not produce the oxygen needed to aid thermal runaway and unlike other lithium battery chemistries will not result in a catastrophic meltdown.

100% COBALT FREE – No rare earth elements

NCM and other lithium ion chemistries that contain rare earth elements such as Colton or Cobalt produce oxygen and toxic fumes when ruptured, leading to fire. Dakota Lithium does not contain rare earth elements, and does not produce oxygen or a fire.

CERTIFICATIONS – Tested and certified for safety and reliability

Dakota Lithium batteries are UN 38 certified and built from grade A cells. Dakota Lithium’s cells are UL1642 certified and have been tested per IEC62133 standards. UN Manual of Tests and Criteria certified, and meets all US International regulations for air, ground, marine, and train transport. Select battery models are ISO Certified ISO 9001:2008 Quality Management System ISO 14001:2004 Environmental Management System for use in industry applications. IEC62133 certifications and additional laboratory services are available as required by our OEM clients.

INSTALLATION CARE – Treat your batteries right

When proper installation and battery care is followed, your LiFePO4 battery will be safe and reliable for many years. This includes making sure all connections are tight and proper wiring sizes are used, compatible chargers and charging components are used, and the batteries are used for purposes that they are designed for.

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