Deep Cycle Battery FAQ. Agm battery minimum voltage

Do I need a special charger for an AGM battery?

Going by Meriam Webster’s definition, a special charger is called for when charging any battery type. In the early days of AGM batteries, when almost all the existing chargers ran on hand wound timers, and could go on charging indefinitely, you very much needed a special charger. When you plugged a battery into one of those dinosaurs, it was constant current, constant voltage, until the electrolyte had a good boil!

Fortunately, there’s a huge offering of various types of chargers in the marketplace today, some better, some worse. We’ll do a quick review of what to look for when choosing the right charger.

AGM Charge Profile (Algorithm)

First, look for a charger that has a specific setting for AGM. It’s best to avoid chargers that claim to charge any battery with one algorithm. Most “one size fits all” products typically only do a mediocre job at best when they try to account for everything under one umbrella.

Amp Output

Second, you need to right-size the charger to go with the capacity of your battery bank. The rule here is a minimum of 10%, but Fullriver recommends 25% of rated capacity in amps for circuits in parallel. For example, if you’re using our DC55-12, this battery has a capacity of 55Ah. You will want to find a charger that puts out at least 5.5 amps, but ideally 13-14 amps. If you have 2, DC55-12’s in a parallel string (12V, 110Ah) you’ll need at least 11 amps, but better if you have 22 amps. Conversely, you don’t want to throw too many amps at the battery, or you’ll run the risk of an early failure. While 25% of rated capacity is ideal, we don’t recommend more than 30% if you need to charge a bit faster. Why? It has a lot to do with surface area. Imagine trying to fill a tea pot with a fire hose.

Phased Charging

Third, if it’s a reputable charger, it will charge the battery in phases to ensure the battery is fully and efficiently charged every time. A prominent example of a single-phase charger would be the alternator in car or truck. An alternator was primarily designed to top-off the vehicle battery after it fulfilled its primary task of starting the vehicle. A car’s alternator lacks the distinctive phases of absorb and finish/float that ensure a battery is balanced and fully charged, especially important in charging a deep-cycle battery. The charger should have at least 3 phases of charging, Bulk, Absorb, and Finish/Float. Some chargers will have a recovery phase in case the battery is inadvertently over-discharged and showing very low voltage.

Voltage Parameter

Finally, attention should be given to the voltage of a given charger at each phase of the charging cycle. AGM in general, and Fullriver AGM in particular takes a bit higher voltage range in the first two phases of charging (Bulk and Absorb) than a gel type battery but needs a lower float/finish voltage. Most charger makers readily share their voltage for each phase of charging. If you don’t see it anywhere obvious, a simple email to the manufacturer will usually do the trick.

The table below shows Fullriver’s acceptable voltage range, with the numbers in bold being our recommended voltage:

In summary, we have seen that pairing the right sized charger and battery can make a great difference in charging a battery as

The impact of these voltages will have less of an impact in lighter applications like RV and will be more critical in heavy use applications like golf/ev.

Fullriver Can Help

Fullriver offers a wide range of chargers with verified algorithms to ensure great charging results. If you’re having trouble finding the right charger for your application, please contact us and we will point you in the right direction.

We want to hear from you. Tell us your charging story. Did you know so much went into charging a battery?

Deep Cycle Battery FAQ

Flooded lead acid (wet cell) batteries are one of the most common types of battery for deep cycle applications. The major difference between the wet type of battery and the sealed kind is that the end user is able to replace water lost through gassing via the vent caps in the top of the battery. The flooded battery has been around for a very long time but remains popular because it has a good balance between price and performance. A gel or AGM cell battery is generally somewhere around twice the price per amp hour that you would find in a flooded battery. Flooded batteries do require a lot more maintenance than their sealed lead acid counterparts because the batteries are not recombinant the water is lost through the top of the vent caps while charging. Replacing this lost water can sometimes be an onerous task, but it is a necessary one to get the most out of your battery.

What is a Sealed Lead Acid battery (VRLA’s)

Sealed Lead Acid batteries are often referred to as being maintenance free or valve regulated. In a sealed lead acid battery the unit is sealed, meaning that water loss is kept to a bare minimum and also that you needn’t put any water into the battery. Most of the sealed VRLA batteries are recombinant which essentially means that the water lost through the venting of hydrogen and oxygen in a flooded battery is the most common types of Sealed Lead Acid or SLA batteries that we carry are the AGM (Absorbed Glass Mat) batteries; another is the GEL type of battery.

AGM batteries have a very fine Boron-Silicate glass mat in between the plates inside the battery. The mats are about 95% filled up with electrolytes rather than completely saturated. The considerable advantage of this type of battery is that they can be operated in almost any orientation and will even function underwater. They will also never leak, even if punctured.

GEL batteries have the electrolyte stored in a gel form; this also won’t spill out even if the batteries are broken and also prevents the stratification that other battery types can have. Gel cells, however, do have some limitations; they take a slower charge than a comparable sized AGM battery. If they are overcharged voids can form in the gel which permanently reduces the battery capacity.

For deep cycle applications however the Sealed Lead Acid type of battery can be a great deal more expensive than a comparable Flooded Lead Acid battery. However, there are times when a sealed battery will better meet your needs than a flooded battery would. Particularly marine applications where stability isn’t always a given, and ventilated spaces are hard to come by are often well tailored to a sealed lead acid battery. One other advantage that AGM and Gel batteries have over flooded types is the low self discharge rate. Where a Flooded battery will lose about 13% of its charge in a month, a Gel or AGM will lose 1%.3%.

What are the differences between a starting and deep cycle battery?

Generally speaking, there are two different types of lead acid batteries, Starting and Deep Cycle. If a starting battery is routinely deep cycled (discharged below 20%-50% of max capacity), it will generally fail after 30-150 cycles. The same starting battery will last for thousands of cycles if it is just used normally (2%. 5% discharge).

  • Starting batteries are generally designed to start some form of an internal combustion engine (car, truck, boat, etc). In a starting battery, you will find more lead plates, thinner and often made of a lead sponge similar looking to a foam sponge. This sort of arrangement means that the plates have much more surface area in the solution than a Deep Cycle battery and allow them to draw larger currents much quicker than a Deep Cycle battery.
  • Deep cycle battery, on the other hand, have much thicker plates and, they are solid, not sponge. These thicker plates have less surface area and thus less of the instant power that a starting battery needs. They are designed to be discharged down to 20% of their maximum charge repetitively. The thicker lead plates allow for this as they are much sturdier than their sponge counterparts.
  • Cold Cranking Amps (CCA) is an indicator of the amount of current a battery can deliver for 30 seconds at zero degrees Fahrenheit without dropping below a specified cutoff voltage (normally 10.5 volts). The cranking amps a battery can produce changes with temperature. The warmer it is the more Cranking Amps a battery will produce.

You can use a Deep Cycle battery as a starting battery provided that you take into account the lower CCA of a Deep Cycle battery. As a rule of thumb, it’s a good idea to upsize the battery by about 20% to deliver the same amount of cranking amps from a deep cycle battery. Also, the self-discharge rate of Sealed batteries is a lot less than flooded lead acid types.

How long will my battery last?

How long a battery will last depends hugely upon the way it is used and how well the battery is maintained. Both overcharging and undercharging will have serious adverse effects on the lifespan of a deep cycle battery. In particular, you can seriously shorten the lifespan of a battery if it is used in a deep cycle application that it was not designed for. An example of this would if you were to use an automotive starting battery as a deep cycle battery.

General expectations for batteries if deep cycled (these are just approximate guidelines):

  • Starting battery (Automotive battery etc) : 3-13 months
  • Marine Battery : 1-6 years
  • AGM Deep cycle: 4-7 years
  • Gel Cell Deep Cycle: 2-5 years
  • Flooded Lead Acid Deep Cycle Battery (L16-RE etc): 4-8 years

The main things that you can do to ensure you get the maximum value out of your deep cycle batteries are to keep them maintained. This means keeping them watered to the appropriate level, trying to prevent them from discharging them more than 50% of their total capacity and having appropriate charging systems in place. The charging is of special importance because both over and undercharging will severely limit the life of your batteries, also if your batteries will see an extended period without being used you should ensure they are routinely checked, cleaned and fully charged before being stored. Also in some cases, it can be a good idea to put your batteries on a maintenance charge over long periods of disuse.

Battery Cycles vs. Battery Lifetime?

Often the lifespan you can expect to get out of your battery is referred to in terms of cycles. A battery cycle is one complete discharge and recharge cycle. The discharge state of a battery is often measured in Depth of Discharge (DOD). This refers to how far down the battery has been taken, for instance, a battery that has 25% of its capacity remaining would be said to be at 75% DOD. The lifetime of a battery is directly related to the depth of the discharge that it regularly experiences. Lead acid batteries are fickle things. If you subject a deep cycle battery to 80% DOD on a regular basis you will get roughly half the life out of your battery than if you were to cycle it to 50% DOD. While this doesn’t mean that you can’t go down to 80% DOD you should generally try to design your battery banks to allow for cycling at around 50%. Conversely there is also an upper limit on the DOD of a battery, usually, a battery that is only regularly cycled down to 5% or less will not last as long as a battery cycled to 10% or more. This is because on smaller cycles the Lead Dioxide can clump up around the positive plates. On heavier discharges, this would be more of an even film.

What does Equalizing my batteries entail and when should I do it?

Equalizing a lead acid battery is the practice of applying a controlled overcharge in order to prolong the battery life, restore lost capacity and to make the battery more efficient. Batteries require equalization because as a battery is cycled (discharged and recharged) a small amount of lead sulfate remains on the lead plates. When you use a three stage charge the degree of sulfation is lessened, but not entirely eliminated. If this sulfate is left on the lead plates it will crystallize, once enough of these crystals have built up on the lead plates they can lead to lowered capacity and lower the amount of power the battery can produce. Also over the lifetime of a battery, the electrolyte solution can tend to stratify, forming layers inside the battery. This can cause the acid near the top of the cell to be more dilute than the acid at the bottom. An equalizing charge is essentially a controlled overcharging of the batteries which will allow the sulfate on the lead plates to recombine into sulfuric acid, it will also break loose any crystallized sulfate on the plates which will then fall to the bottom of the battery. It’s always a good idea to not fill your batteries before you equalize, the electrolyte will expand during equalization and if the batteries are too full they could overflow. There should be enough liquid to cover the plates and not much more.

Below is a table from Trojan batteries website detailing their recommended charge levels and durations:

Trojan Batteries recommended charger voltage settings:
System Voltage

Important things to note before equalizing your batteries:

  • Any DC loads on the batteries should be turned off, the greater than the normal voltage that occurs during equalization can cause damage to anything attached.
  • Leave the caps on the cells, these caps are vented and will prevent your electrolyte splattering onto the top of the battery. Sometimes laying a paper towel over the tops of the batteries can be a wise precaution also.
  • If a battery starts to spit acid stop the charging process immediately
  • Batteries should be fully charged and at room temperature before you equalize

Equalizing steps:

  • Make sure the batteries are fully charged, at an even temperature and are flooded acid.
  • Take off any loads from the batteries
  • Connect your charger
  • Set the charger for the correct voltage
  • Start to charge your batteries
  • The batteries should begin gassing and bubbling
  • Take specific gravity readings every hour or so
  • When the gravity values no longer rise during the gassing stage the equalization is complete

How often should I refill my batteries (or do I even need to)?

Flooded batteries have to be watered periodically to maintain their performance and increase their longevity. As the chemical reactions take place some of the water is lost as gas from the vent caps. This means that the acid in the battery will eventually get below the level of the lead plates. Luckily as it is just water that is being lost (hydrogen and oxygen) all that has to go back in is pure water.


Learn more about the best Deep Cycle Batteries for Solar, Camping, Caravan, Camper Vans, Camper Trailers, Motorhomes, Marine, 4WDs, RV’s Off Grid Solar with the experts at Aussie Batteries and Solar WWW.AUSSIEBATTERIES.COM.AU

This guide answers our customer’s most frequently asked questions about Deep Cycle Batteries. This guide includes information on how AGM and Lithium deep cycle batteries work. And you can learn about deep cycle battery terminology. Learn more about the different deep cycle batteries used in renewable energy storage systems and develop your understanding of the different Deep Cycle Battery chemistry types such as Gel Deep Cycle, AGM Deep Cycle, Lithium Deep Cycle Batteries, and more! If you need expert, no-obligation advice about Deep Cycle Batteries, you can Free Call 1800 853 315

Deep Cycle Batteries Guide for Energy Storage. What is a Deep Cycle Battery?

If you’re looking for a battery for solar and renewable energy or a battery for camping applications, you’re looking for a Deep Cycle Battery nine times out of ten. A Deep Cycle Battery comes as an AGM battery or Lithium battery and is the best battery for Solar, Camping, Caravan, Camper Vans, Camper Trailers, Motorhomes, Marine, 4WDs, RV’s Off Grid Solar because Deep Cycle Batteries are very efficient energy storage units that allow you to store and use power!


For 4×4 or recreational use and any solar camping setups, the best deep cycle battery has traditionally been AGM Batteries due to their price. For the best battery performance and serious off-road adventure enthusiasts, Lithium Batteries are currently the best deep cycle battery option your money can buy. Both AGM and Lithium Deep Cycle Batteries work when a chemical reaction develops a voltage that results in electricity. Deep Cycle Batteries are designed to be ‘cycled’ (discharged and recharged). Hence, while a car battery aims to deliver a burst of energy for a short period, a deep cycle battery gives power at a steady rate for an extended period. In the context of renewable energy, batteries usually mean deep cycle batteries. The two best options for deep cycle battery power are AGM Batteries and Lithium Deep Cycle Batteries are presently the best because of their weight and ability to draw more power from the battery cells.

Can I Use Solar Panels to Charge My Deep Cycle Battery?

YES. in fact any type deep cycle battery can be charged with solar panels. Make sure to use a solar charge controller for deep cycle solar batteries to regulate the charge or add an Ardent Battery Box with Anderson Plug Connections. An Anderson style plug is a moulded, heavy-duty connector designed for high current 12V circuits. They are commonly used to create a safe and secure power connection between a battery and the solar panels. Indeed, most caravans and campers these days have an Anderson style plugs installed from factory. For Lithium Deep Cycle Batteries you need to make sure the open voltage of the solar panel is below 18V for a 12V battery. It is best if your solar panel has a voltage regulator to stop charging at 14.4V or (LiFePO4) setting of 14.6V.

If you charge your lithium deep cycle battery above 15V for 12V battery, the BMS inside the battery terminal will turn off.

The cut-off voltage settings will vary slightly depending on current levels, temperature and part tolerances. To turn ON the battery again, disconnect the charging source and let the battery rest for several seconds (~30 sec). In the event the 12V battery had voltages higher than 18V when turned off, the internal BMS could be damaged and will not turn ON.

Can I Start My Car With A Deep Cycle Battery?

NO. Deep cycle batteries aren’t designed to deliver high currents to start a car. Using one could damage the battery or the car. Make sure you stick to a starting battery for this purpose.

Can I Connect Different Deep Cycle Batteries?

NO. Try to only connect batteries of the same type, model, capacity, and age. For example, if you want to connect your deep cycle battery with another one to increase power output, make sure the second battery meets the mentioned criteria.

Why is the cheapest eBay battery not your best option? Every year, we speak to hundreds of customers who find out that eBay may be a great place to get a quick bargain. AGM Batteries or Lihium Batteries are one of the products that you are much better off getting from a reputable retailer like Aussie Batteries, who can provide you a competitive warranty and exceptional technical support.


Lithium ion batteries are 50% lighter than AGM batteries and have a usable capacity of 90.100%. They also have the fastest recharge rate and extremely long cycle life — often around 2000-5000 charge cycles. A LiFePO lithium Ion deep cycle battery also offers constant voltage over any rate of discharge. This means your lithium battery powered camping lights won’t dim slowly as the battery loses charge. Once there’s no more power, the lights will just go out. The most recent type of lithium battery is Lithium Iron Phosphate (LiFePO4). LiFePO4 batteries are frequently used in deep cycle applications — such as solar energy banks and backup power systems. A quality lithium deep cycle battery is lightweight, compact, maintenance-free with excellent usable discharge capacity, fast recharge rate, and constant voltage. However, it’s much more expensive than AGM batteries and you need to make sure it has a superior battery maintenance system (BMS).

Note: In a LIthium Deep Cycle Battery the BMS monitors the battery’s state and ensures the safety of operation. All Aussie Batteries Lithium range are equipped internally with superior BMS systems up to 150AMPs allowing users to get max power!

100% Environmentally-Friendly Energy

Save on Weight as Lithium are 50% lighter

Draw more usable battery power

Getting the best Deep Cycle Battery will depend on what you want to use the battery for, and it also means deciding on a battery solution for your setup. Aussie Batteries stock a range of recreational and commercial batteries for all deep cycle battery applications such as camping, boating and off-grid applications. Aussie Batteries stock Australia’s most extensive range of Deep Cycle Batteries, including Lithium Batteries and AGM Batteries and the battery range is built specifically for Australia’s outback environment.


Aussie Batteries and Solar are the experts in gearing you up with a camping power solution that will suit you and the way you like to camp. With decades of experience under our belts, we are all about providing the best deep cycle battery products, best battery and free expert battery advice. to help you get the best deep cycle battery for your adventures around Australia! Using a 12V lithium battery will upgrade your camping battery system, especially if you are going for long periods without electricity. Lithium batteries are high-quality deep cycle batteries and a lithium deep cycle battery gives unrivalled performance and superior battery life perfect for use in a range of power applications.12V lithium battery options deliver longer-lasting power, and they are built to survive and thrive in Australia’s toughest camping, caravan and 4WD conditions. easily swap your older style AGM Battery for the newer technology of Lithium Deep Cycle Batteries.

Lithium Batteries are the perfect AGM Upgrade:

Use your Lithium Battery the same as AGM

Ideal for weight-sensitive and high-vibration

Upgrade from AGM. Simply drop-in

Get 5 times faster charging

50% saved weight; and increased usable power

Supports in-series and parallel connection


An AGM battery is a type of Valve Regulated Lead Acid (VRLA) battery. AGM is short for Absorbent Glass Mat, which refers to the thin fiberglass mats placed between the lead plates. The glass mat absorbs electrolyte, keeps it from moving and spilling, and acts as a damper between the lead plates. The damping action of the glass mat makes the battery shock and vibration resistant, with the ability to withstand cold temperatures. An AGM deep cycle battery has low internal resistance and charges faster than a flooded battery or gel battery. It has a 95% charge efficiency and an 80% Depth of Discharge (DoD). An AGM battery’s many advantages include being maintenance-free, position insensitive, durable and fast-charging compared to flooded cell batteries.

Why the GIANT POWER 140AH AGM is the Best-Selling AGM Deep Cycle Battery in Australia:

This 140AH AGM Battery is best of the best for most 12 Volt Setups and power requirements customers ask for and is an Australian Tier 1 top-rated deep cycle battery product with thousands of 5 star reviews.

Compatible with all major battery boxes

Industry Leading Australian 5 Year Warranty.

Best-quality 12 Year Designed Service Life.

High-Quality Bolt Terminal Connections.

Australian Owned and Operated Company.

Voted best AGM Deep Cycle Battery Australia!

Aussie Batteries stock the most comprehensive range and best quality AGM Batteries in Australia.

The best traditional or older style Deep Cycle Battery is AGM Batteries, which use thicker battery plates and denser active internal material. Deep Cycle AGM Batteries are designed to withstand repeated charge and recharge cycles and are popular for Australians looking for reliable energy solutions where weight doesn’t matter. AGM Deep Cycle Batteries are also known as Absorbed Glass Mat (AGM), and they use technology that suspends the free electrolyte within a highly porous (AGM plate). The plates’ quality means the battery is constructed using glass fibre mat separators. AGM battery plates help eliminate the hazards associated with acid spills or leaks. They allow for a sealed maintenance-free design that avoids any need for regular topping-up of an electrolyte. Try our Deep Cycle Calculator to determine your energy requirements free call our team on 1800 853 315

What are the benefits of AGM Deep Cycle Batteries?

AGM Batteries are sealed and are easy and safe to transport. They never need topping up with water. They can be safely mounted inside a boat, car, caravan, motorhome, or recreational vehicle.

Absorbent Glass Mat (AGM) is a deep cycle battery in which the electrolyte is absorbed into a fibreglass mat. You will find that the plates in an AGM Battery are flat like wet cell lead-acid batteries, or they may be wound into a tight spiral. The internal resistance of AGM Batteries is lower than traditional cells; they can handle higher temperatures and self-discharge more slowly than other types of batteries. AGM Deep Cycle Batteries have a release valve activated when the battery is recharged at high voltage. This valve activation allows a small amount of active material to escape. AGM Batteries typically have gas diffusers built into them that allow for the safe dispersal of any excess hydrogen created during charging. The main benefits of AGM Deep Cycle Batteries and their popularity are that they are classed as maintenance-free batteries. Unlike regular lead-acid batteries that should be kept in an upright position avoiding acid spills and to ensuring the plates are sitting in the electrolyte; AGM Deep Cycle Batteries can generally be placed in any orientation, though it always best to speak to an expert to make sure your battery set-up is correct and wont void any warranties. Due to their very low internal resistance AGM Deep Cycle Batteries can fully charge at a lower voltage and accept a much larger load charge current. When charging from a standard car/truck alternator, these batteries may be fully charged in about three hours! AGM batteries can also be discharged ‘deeper’ than conventional deep cycle batteries without significant damage. For example, AGM Batteries only self-discharge at the rate of up to 3% per month, and even after 12 months sitting idle, as long as they have been cared for, they can be recharged and put back into full service without any significant damage. AGM batteries were originally developed for the military, and because of this, they are very robust.


  • Run appliances when camping away from power
  • Power 12V fridges, lights or any 12V appliances
  • Excellent for use with a solar panel for charging
  • Perfect for running in a dual battery system
  • Superb for use in 4×4 and marine conditions
  • Designed Service Life 15 years
  • Ideal for frequent cyclic discharge
  • Exceptional deep discharge recovery
  • Low self-discharge characteristics


Lithium 12V Deep Cycle Batteries are purpose-built for long-use applications if you need reliable energy. Unlike gel or AGM batteries, a LiFePO4 Lithium Battery is exceptionally portable, weighs 50% less, and has a longer shelf-life. Using forward-thinking technology that is powering electric car giants like Tesla. Upgrade to a good LiFePO4 battery that can also withstand any damage without exploding, keeping you and your family and friends safe in any event when you’re out exploring the world. LiFePO4 batteries are incredibly safe; they are light and available for various uses. Lithium Deep Cycle Batteries are arguably the safest way to provide power for your camping trip. They don’t heat up when charging and discharging and can provide a consistent energy source until the last volt is used.

  • Light Weight: About half the weight of an equivalent SLA or AGM battery
  • Environmentally Friendly: Non-toxic, contains no acid, can be installed in any direction. Up to 80% capacity for 2,000 cycles in recommended conditions.
  • Steady output voltage: no memory effect, vibration and shock resistant, will continue to work efficiently in high temps
  • Charge with solar panels on the road

What is the best set-up for a 36 volt trolling and starting?

We have options available including three 12V 50Ah or 75Ah batteries. Get Expert advice 1800 853 315

What is the best set-up for a 24 volt trolling and starting?

If you fish tournaments, We suggest anything above 100Ah batteries for trolling and a 140Ah for starting. If you are a weekend fisherman you can use the 50Ah battery. Get Expert advice 1800 853 315

Deep Cycle Battery Ratings: Deep Cycle batteries are generally rated in Volts and Amps.

  • Amp-hours (Ah) are the rated capacity available in chemical energy inside a battery that is converted into electrical energy.
  • Amps also refer to the amount of energy that the battery can store, or, it can be called the discharge rate. The Discharge rate measures the time it takes to discharge a battery before it needs recharging again.

Here are no-load typical voltages vs state of charge

(figured at 10.5 volts = fully discharged, and 25 degrees C).

deep, cycle, battery, minimum, voltage

These Voltages are for a 12-volt battery system. For 24 volt systems, multiply by 2; for 48 volt systems, multiply by 4. 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, and you have to let the battery sit for a while.For the most extended 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 essential to realize that voltage measurements are only approximate. The best determination is to measure the specific gravity, but this is difficult or impossible in many batteries. Note the significant voltage drop in the last 10%.

What Do Deep Cycle Battery Specifications Mean?

Say you’ve got a deep cycle AGM battery and its specifications list that it produces:

100Ah at 20 hours, rated 1000 full cycles at 80% DoD

Battery Capacity:

  • The Amp Hour (Ah) denotes battery capacity and shows how much current can be delivered for a specific time.
  • A 100Ah battery at 20 hours means it can produce 5 Amps for 20 hours (100/20 = 5). Deep cycle batteries are typically rated for a 20-hour discharge.

The main thing to understand is that if you’re going to load more appliances, you’ll need a larger AH battery capacity or an upgrade to Lithium for more available energy draw.

The discharge cycle defines how many times a battery can be discharged and charged without reducing performance or capacity. 1000 full cycles simply mean it can be charged and discharged 1000 times. The more full cycles there are, the longer the battery life.

Depth of discharge determines how much of the battery can be discharged safely compared to its original capacity, before it must be recharged. Deep cycle batteries are meant to discharge more of their energy. An 80% DoD means the battery can discharge down to 20% of its capacity.

Lithium Batteries State of Charge (Technical Information)

The voltage of all conventional deep-cycle batteries (as well as AGMs) constantly falls as they discharge. This is typically from 12.75–11.4 volts. The voltage also falls as load increases. Any LiFePO4 deep cycle battery will provide the continuous peak power required. It will also maintain substantially constant voltage regardless of the load. That voltage is likely to be from 13.1–12.9 volts in practice. Readers with a physics background will realise this provides a correspondingly higher output of about 10% (in terms of watt hours).

Lithium Deep Cycle Batteries have multiple advantages over standard AGM batteries for energy storage:

  • Substantially Lighter – Lithium-ion batteries are just a fraction of the weight of the original AGM battery.
  • Powerful – Lithium-ion batteries operate at a higher voltage than standard AGM batteries or lead-acid batteries, dropping to just 12.5V when only 20% of the battery capacity is used. Lithium-ion batteries provide over 12.8V even when only 20% is left.
  • Low Self-Discharge Rate – Lithium battery chemistry loses less than 3% of charge per month; you can go for several months without worrying.
  • Environmental Friendly – Lithium batteries contain no toxic substances. There is no poisonous lead or corrosive sulfuric acid, and as a result, no possible way for an explosive gassing event that is common with lead-acid batteries. In addition, there is no need to maintain acid levels or worry about venting as traditional lead-acid batteries do. Lithium batteries’ only maintenance requires ensuring that the battery never drains beyond 90% to ensure optimal life.
  • Long-Lasting – Lithium-ion batteries can provide 8-15 years of use, easily exceeding the life of any lead-acid battery. Battery life depends on proper operation and maintenance, so use common sense and ensure the battery does not drain beyond 90% discharge. If you are replacing a lead-acid battery in two years or less due to severe cycling damage, you will save money; in the long run, moving to lithium-ion as the BMS will automatically protect the battery.
  • Fast Recharging – Lithium batteries can accept a charge current up to 5 times faster than a lead-acid battery. The charge efficiency is about 75% for lead-acid compared to 97% for a lithium battery. That means less energy is needed to charge.

Charging Your Deep Cycle Battery

Dependable performance and long service life depend upon correct charging. Faulty procedures or inadequate charging equipment result in decreased battery life and unsatisfactory performance. Selecting suitable charging circuits and methods is as important as choosing the correct battery for your application. To obtain maximum service life and capacity and acceptable recharge time and economy, constant voltage-current limited charging is recommended. During charge, for AGM batterues the lead sulfate of the positive plate becomes lead dioxide. As the battery reaches full charge, the positive plate begins generating dioxide causing a sudden rise in voltage due to decreasing internal resistance. Therefore, a constant voltage charge allows detection of this voltage increase and thus control the current charge amount. LITHIUM can be charged by most deep cycle chargers and don’t need a special battery charger! Lithium batteries are manufactured with a built-in high-quality battery management system (BMS) that allows for most charger settings (20A)min (except flooded) to be used A standard Gel, or AGM charger is safe and suitable but will only charge the battery to 97% If you want a lithium specific charger add an ARDENT 12V LITHIUM CHARGER

What’s The Charging Time For Deep Cycle Batteries?

The actual timing depends on several factors, including the battery capacity, age, battery charger, on average, here’s how long they’d take to charge:

  • Flooded lead acid battery: 8-16 hours
  • AGM Battery: 5 hours
  • Gel battery: 5-10 hours
  • Lithium Battery: 2-3 hours

Battery Charging and Deep Cycle Battery Maintenance

Batteries should not be stored in a discharged state or at elevated temperatures. If a battery has been discharged for some time or the load was left on indefinitely, it may not readily take charge. To overcome this, leave the charger connected, and the battery should eventually begin to accept the charge.

Continuous over-or undercharging is the single worst enemy of any Deep Cycle Battery. Caution should be exercised to ensure that the charger is disconnected after cycle charging or that the float voltage is set correctly.

For Lithium, it is essential to charge immediately as these batteries are discharged for transportation. Much like your mobile phone battery, you should immediately charge any Deep Cycle Battery before the first use. An AGM battery must be charged within six months after receipt to account for storage from the date of manufacture to the date of purchase. Otherwise, permanent loss of capacity might occur as a result of sulfation. To prolong shelf life without charging, store batteries at 10′C or less.

Unlimited current charging can cause increased off-gassing and premature drying. It can also produce internal heating and hot spots resulting in shortened service life. Too high a charge current will cause a battery to get progressively hotter. This can lead to thermal runaway and destroy a battery in as little as a few hours.

Caution: Never charge or discharge a battery in an airtight enclosure. Batteries generate a mixture of gases internally. Given the right set of circumstances, such as extreme overcharging or shorting of the battery, these gases might vent into the enclosure and create the potential for an explosion when ignited by a spark. Generally, ventilation inherent in most enclosures is sufficient to avoid problems.

High voltage strings of batteries in series should be limited to twenty 6 volt or ten 12 volt batteries when a single constant voltage charger is connected across the entire string. Differences in capacity can cause some batteries to overcharge while others remain undercharged, thus causing premature ageing of batteries. It is, therefore, not advisable to mix batteries of different capacities, make, or age in a series string.

Recharge time depends on the preceding discharge depth and the charger’s output current. To determine the approximate recharge time of a fully discharged battery, divide the battery’s capacity (amp. hrs) by the rated output of the charger current (amps) and multiply the resulting number of hours by a factor of 1.75 to compensate for the declining output current during charge. If the amount of amp. Hrs. Discharged from the battery is known; use it instead of the battery’s capacity to make the calculation.

Overcharging Deep Cycle Batteries:

As a result of too high a charge, excessive voltage current will flow into the battery after reaching full charge, causing decomposition of water in the electrolyte and premature ageing.

At high rates of overcharge, a battery will progressively heat up. It will accept more current as it gets hotter, heating up even further. This is called thermal runaway, and it can destroy a battery in as little as a few hours.

Undercharging AGM Deep Cycle Batteries:

If too low a charge voltage is applied, the current flow will stop before the battery is fully charged. This allows some of the lead sulfate to remain on the electrodes, eventually reducing capacity.

Batteries stored in a discharged state, or left on the shelf for too long, may initially appear to be “open-circuited” or accept far less current than expected. This is caused by a phenomenon called “sulfation”. When this occurs, leave the charger connected to the battery. Usually, the battery will start to accept increasing amounts of current until an average current level is reached. If there is no response, even to charge voltages above recommended levels, the battery may have been discharged for too long to recover.

Capacity Resistance in Deep Cycle Batteries

Amp-Hour Capacity

All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour or ten amps for 1/10 of an hour. It is amps x hours. If you have something that pulls 20 amps and uses 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 for nearly all deep cycle batteries is the “20 hour rate”. A 10Hr rating is widely used in the USA. Therefore many batteries can have 10hr, 20hr or both specifications stated. The 20hr rating means that it is discharged down to 10.5 volts over 20 hours while the actual amp-hours it supplies are measured. Sometimes ratings at the 6-hour rate and 100-hour rate are also given for comparison and 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 to make the battery look better than it is. Still, it is also helpful for figuring battery capacity for long-term applications like backup, solar, and camping amp-hour requirements.

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Lithium Battery Vs AGM Battery

All batteries degrade over time, but lithium-ion batteries consistently outlast AGM batteries. Factors like a more significant depth of discharge make lithium-ion batteries more resilient and help these batteries go up to six times the life cycles of AGM alternatives. Choosing the right Deep Cycle Battery for your application is important.The size and type of Deep Cycle Battery that you select is dependent on the application and operating conditions. It is important to ensure there is sufficient battery capacity (Amp Hours) to power the equipment you intend to use.

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Comparing Lithium deep cycle to AGM and lead-acid batteries, the benefits quickly stack up. The full Amp Hour capacity of a quality lithium battery can be used without affecting the battery’s life span. In contrast, with an AGM or lead acid, it is recommended that you don’t discharge below 50%. This means that a lithium battery rated at 100 amp-hours is closely comparable to 200 amp-hours of AGM or lead-acid batteries in terms of usable power. Lithium batteries offer improved functionality over their AGM and flooded alternatives in that they can be discharged to a higher level safely than their counterparts, providing more actual useable Amps. Lithium batteries can be safely discharged to a 100% Depth Of Discharge (DOD) (@10.5v), which provides more useable amps vs. a maximum 50% DOD for an AGM to maintain its cycle life. Lithium batteries cost more than AGM batteries to manufacture, and the price of Lithium is not coming down. As Lithium is an Ore product and traded on the stock market alongside gold, platinum and silver this means that the amount and quality used in batteries and the internals directly affects the production cost of the battery. We are talking about the cell quality and rating, internal (BMS) Battery Management System, and the battery’s actual useable capacity.


Lithium batteries are rechargeable batteries in which lithium ions move from the anode to the cathode during discharging and back when charging. They are popular batteries for use in consumer electronics because they provide high energy density, possess no memory effect, and slow charge loss when not in use. These batteries come in a wide variety of shapes and sizes. Compared to lead-acid batteries, Lithium batteries are lighter and provide a higher open-circuit voltage, which allows for power transfer at lower currents.

  • Lightweight, up to 50% less than a conventional AGM
  • Lasts 300-600% longer than lead-acid.
  • Lower shelf discharge rate (2% vs. 5-8% /month).
  • Drop-in replacement for your AGM battery.
  • Expected 12-20 years of battery life.
  • No explosive gasses during charging, no acid spills.
  • Environmentally friendly, no lead or heavy metals.
  • Safe to operate!

The term “Lithium-ion” battery is a general term. Many different chemistries for lithium-ion batteries include LiCoO2 (cylindrical cell), LiPo, and LiFePO4 (cylindrical/prismatic cell). The voltage of all conventional deep-cycle batteries (as well as AGMs) constantly falls as they discharge. This is typically from 12.75–11.4 volts. The voltage also decreases as the load increases. However, any LiFePO4 suitable for (and in) use will provide the peak power required. It will also maintain substantially constant voltage regardless of the load. That voltage is likely to be from 13.1–12.9 volts in practice. Readers with a physics background will realise this provides a correspondingly higher output of about 10% (in terms of watt-hours).

What are LiFePO4 (Lithium Iron Phosphate) Batteries?

Lithium Iron Phosphate (LiFePO4) batteries are a type of lithium battery that provide several advantages. LiFePO4 delivers a much higher specific capacity, superior thermal and chemical stability, enhanced safety, improved cost performance, enhanced charge and discharge rates, enhanced cycle life, and a compact, lightweight package. LiFePO4 batteries offer a cycle life of over 2,000 charge cycles!


Each battery is equipped with an internal BMS. Battery Management System (BMS). The BMS in a lithium battery monitors and optimises each cell during charge and discharge. This protects the battery pack from overcharge, over discharge and short circuit. The BMS also allows the balancing of cells within the batteries allowing them to be configured and used in-parallel to increase battery bank capacity for increased power storage. That is why when buying a battery you should only use a trusted supplier which make choosing the right battery essential. Weight saving is where Lithium Batteries come into their own. An equivalent (useable capacity) Lithium battery will take up ½ of the physical weight space of an AGM battery, which is excellent if you want to hide it somewhere. Alternatively, get double the power for the same area.

Another significant benefit of lithium is that they are considerably lighter than a similar-sized AGM or lead-acid battery. Commonly, most touring vehicles or trailers are overloaded with a whole host of essential things like luggage, accessories, recreational gear, people, and pets, so you can cut down battery weight by up to 50% by choosing lithium batteries, it’s often a no brainer. Especially when multiple auxiliary batteries are part of the system, having a lighter setup can be crucial.

Aside from the weight savings, Lithium batteries also have significantly quicker re-charge vs. AGM batteries. The low resistance in the Lithium cells allows the battery to accept the total output from the charger. With a 30 Amp charger, a 100Ah Lithium battery can be fully charged from flat to full in just over 3 hours vs. 10 for a 100Ah AGM battery. This is a considerable advantage with solar in that every amp that your solar panels produce goes directly into the battery.


What happens if I charge my lithium deep cycle battery too high?

If you charge your lithium deep cycle battery above 15V for a 12V battery, the BMS inside the battery terminal will turn off. The cut-off voltage settings will vary slightly depending on current levels, temperature and part tolerances. To turn ON the battery again, disconnect the charging source and let the battery rest for several seconds (~30 sec). It should come on. If the 12V battery has voltages higher than 18V, the internal BMS is damaged and will not turn ON. Battery life for a lithium battery can be enhanced by not discharging the battery to 1Ah capacity or BMS lower voltage cut-off settings. Discharging down to BMS lower voltage cut-off settings can quickly decrease the life of the battery. Instead, we advise discharging down to 20% capacity remaining then re-charging the battery.


Deep cycle batteries are a great source of renewable energy, particularly when they are used in conjunction with a solar charging kit. If you need power, yet you are not tapped into the power grid (I.e.: receiving an electricity bill for the power you’re using) then you need a deep cycle battery. Deep cycle batteries are perfect for:

  • Camping and caravanning
  • 4WDing
  • Off grid living
  • Holiday houses
  • Mobility scooters
  • Golf carts
  • Kids ride on cars
  • Forklifts
  • Boats
  • Sheds
  • Standby power for Uninterruptable Power Supply (UPS)

Know your current draw power needs

Before you buy a battery, whether Lithium or AGM, you probably need to consider your maximum current draw, based on all the things you could run off the system. A 100AH battery can run a 1000W inverter (divide wattage by 10 to get the amps required to run the inverter) using 1000W of power. But if using the 1000W load on the inverter, you put the maximum load on your battery, so you’ll need bigger batteries if you are running anything else concurrently. If you don’t forecast your current draw correctly, your battery may appear to handle the higher draw. Still, in reality, you will cook the battery’s cells as it struggles to deliver the power required safely, which may mean you kill your battery much sooner than you should. AH gives you more energy!

Cycles vs Life. AGM Deep Cycle Battery Technology

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 regularly. Those same batteries are rated at less than five years if cycled to 50%. For example, most golf cart batteries are rated for about 550 cycles to 50% discharge, equating to about two 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%. There are some practical limitations on this – you don’t usually want to have a 5 ton pile of batteries sitting there to reduce the DOD. The most practical number to use is 50% DOD regularly. 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 the Lead Dioxide tends to build up in clumps on the positive plates at very shallow cycles rather than an even film.

Do’s Donts for proper use of your Deep Cycle Batteries

Alternators Generators what you need to know about using them with a Deep Cycle Battery

Alternators work reasonably well with AGM batteries in a general car or van. However, they are not battery chargers and will never fully charge a Deep Cycle Battery, so it’s best to use a battery charger when main power is available to top up the battery charge and avoid reduced battery life from sulphation. Note that alternator output voltages are often reduced by cable/wiring runs and Dual Battery systems, so care needs to be taken to measure the voltage received at the battery across its terminals to ensure its adequate to charge the battery fully charged battery.

Conversely, for Gel batteries fitted close to the alternator (under-bonnet with a thick gauge cabling), there is a real risk of damage due to over-charging as the alternator output can be too high for the battery. For this reason, we highly recommend NOT using GEL batteries with car alternators.

Generators Deep Cycle Batteries

Many Portable Generators do not have battery charging circuitry built-in and should be used with care if they provide a DC outlet (although you could plug a battery charger into the 240V socket, it seems a relatively inefficient way to operate). The later models (from Honda etc.) with the built-in chargers can provide a reasonably quick and efficient battery top-up on sites where they are allowed (or off-site), although some users do grow tired of the noise and migrate to solar over time.


Why Deep Cycle Batteries are so popular!!

AGM [Absorbed Glass Mat] VRLA

Sealed Absorbed Glass Mat (Ca/Ca) VRLA deep cycle batteries (also known as starved electrolyte or dry) have a very fine fiber Boron-Silicate glass mat between their flat Lead with Calcium alloy in the positive and Lead with Calcium alloy in the negative plates. The AGM battery was invented in 1980 and first used in military aircraft in 1985.

AGM, or 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. 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:

  • Much safer than wet batteries (due to the hydrogen gas recombination during charging)
  • Do not require water.
  • Lower self-discharge rate (typically 1%-2% per month)
  • Longer service life (approx. 2-3 times life expectancy of Flooded lead acid)
  • Higher resistance to vibration
  • Lower deep discharge failure
  • Less forgiving when accidentally overcharged
  • Higher bulk charge acceptance rate (which means up to a 15% shorter recharge time and reduced cost than Flooded lead acid)
  • Do not require special hazardous shipping.
  • It can be used in saltwater applications
  • Spill proof and can be mounted in virtually any position (because they are sealed)
  • It can be used inside an enclosed area, like the passenger compartment or trunk
  • Greater terminal corrosion resistance

What about 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. 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. Better inverters commonly used in solar electric systems can be set to limit the charging current to the batteries.

Some other disadvantage 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. Water loss can be enough over 2-4 years to cause premature battery death in hot climates. For this and other reasons, we sell few lines of the gelled cells. The newer AGM (absorbed glass mat) batteries have all the advantages (and then some) of gelled, with none of the disadvantages.

Starting, Marine Deep Cycle Batteries

Starting (sometimes called SLI, 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 as much as 80% time after time and have much thicker plates. The significant difference between an AGM deep cycle battery and others is that the plates are SOLID Lead plates – not a 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 buying in some of the discount stores or places that specialize in automotive batteries. The golf car battery is quite popular for small systems and RV’s. The problem is that golf car refers to a size of battery (commonly called GC-2, or T-105), not the type or construction – so the quality and construction of a golf car battery can vary considerably – ranging from the cheap off brand with thin plates up the true deep cycle brands, such as Crown, Powersonic, Trojan, etc. In general, you get what you pay for.

Marine batteries are usually a hybrid, and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette and Concorde, for example) are proper deep cycle. The plates may be composed of Lead sponge in the hybrid, 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. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open – not much of an option.

AGM Battery Plate Thickness

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 (AGM) 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 seven times as thick as auto batteries. The typical golf cart will have around.07 to.11″ 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.

Internal Resistance in an AGM Deep Cycle Battery

deep, cycle, battery, minimum, voltage

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. AGM batteries have resistance levels up to 5 times lower than standard batteries. 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 250 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%. Proper deep cycle AGM’s can approach 98%. The 20-hour rate is the most common for standardizing batteries in Australia, while the USA uses a 10-hour rating system.

The lifespan of Deep Cycle Batteries

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. In extreme cases, it can change to extremes – AGMs can be killed in less than a year by severe overcharging. Gelled cells batteries can be destroyed in one day when overcharged with a large automotive charger. Golf cart batteries can be destroyed without ever being used in less than a year because they were left sitting in a hot garage 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 dry – they are actually filled with acid, the plates formed and charged, then the acid is dumped out. These are 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. But here goes anyway:

  • Starting: 3-12 months
  • Marine: 1-6 years
  • Golf cart: 2-7 years
  • AGM deep cycle: 4-10 years
  • Gelled deep cycle: 2-7 years
  • Telephone (float): 2-10 years. These are usually special-purpose “float services” but often appear as “deep cycle” on the surplus market. Depending on age, usage, care, and type, they can vary considerably.
  • NiFe (alkaline): 5-35 years
  • NiCad: 1-20 years
  • Lithium: 12-25 years

Inverters for Deep Cycle Batteries

An inverter has two functions – to provide an alternating current (ac) voltage rather than the direct current (dc) available from the battery and raise the voltage up to an average of 240V. There are several types of inverters. The most expensive provide a pure sine wave which is preferred for any sensitive equipment, especially laptops. The cheapest simply provides a square wave ac, which is satisfactory with most motors and small chargers for cameras, phones, etc., but not for most laptop computers. There are also intermediate types, “modified sine wave”, which combine many square waves to approximate a sine wave shape. These are usually satisfactory for laptops but often create a lot of radio interference, like the square wave types. Inverters are about 80% efficient. They come in different sizes. A 300W unit will handle most camp requirements but may have trouble starting a laptop (even though the average drain by the computer is much less than this.) A 300W unit is probably a sensible minimum. Bear in mind that Watts = Volts x Amps, so if we draw the total 300 watts, we will require 25 amps from the 12volt battery, plus 20% to account for inefficiency. That’s 30 amps. This will draw from the battery in 1 hour, about the same as all other loads discussed above take in a day. There are also many larger inverters. A 2000W Inverter will provide enough power to run power tools or even an electric jug, but they will draw about 150-200 amps from the battery at full output. That’s as much current as they winch when fully loaded and way outside the comfort zone of any deep cycle battery for long periods. Most 1500w-2000w applications such as microwaves and electric kettles will only run for a few minutes; this will be fine to use with any 100AH battery.

Installing Your Deep Cycle Battery

Fasten batteries tightly and make provisions for shock absorption if exposure to shock or vibration is likely.

When installing the battery within a piece of equipment, fix it securely at the lowest possible point.

The battery should not be attached to any piece of equipment during “burn-in” testing.

Do not apply undue force to the terminals or bend them. Avoid applying heat to the terminals through processes such as soldering.

If soldering to the battery terminals is unavoidable, it must be accomplished within 3 seconds, using a soldering iron no greater than 100 watts.

Do not place batteries close to objects which can produce sparks or flames, and do not charge batteries in an inverted position.

Avoid exposing batteries to heat! Care should be taken to place batteries away from heat-emitting components. If proximity is unavoidable, provide ventilation. Service life is shortened considerably at ambient temperatures above 30°C.

To prevent problems arising from heat exchange between batteries connected in series or parallel, it is advisable to provide air space of at least 0.4″ (10mm) between batteries.

Do not mix batteries with different capacities, different ages or different makes. The difference in characteristics will cause damage to the batteries and possibly to the attached equipment.

Battery cases and lids made of ABS plastic can sustain damage if exposed to organic solvents or adhesives.

For best results and generally acceptable performance and longevity, keep operating temperature range between.40′C and 60′C.

It is good practice to ensure that the connections are re-torqued and the batteries are cleaned periodically.


LiFePO4 batteries store three to four times the electrical energy of conventional batteries of similar size and weight. This is a major benefit for camper-trailers, caravans, campervans and smaller motorhomes: most have limited space and weight carrying capacity. It’s less of a benefit, however, for converted coaches. Most can readily cope with the weight and volume of a 400-750 Ah AGM battery bank that will easily cope with even major RV loads, and at well under half the price.


LITHIUM DEEP CYCLE BATTERIES are designed to give users a 15% quicker charge rate. meaning a Lithium Deep Cycle Battery works silently in the background keeping the food fresh, 12V lights on, drinks cold, tablets or other devices charged!

What Are Some Deep Cycle Battery Features To Consider?

  • Size and weight: Smaller batteries are easier to carry and reduce overall vehicle weight.
  • Voltage rating: Higher voltage batteries should be used for larger loads.
  • Charging time: The smaller the number, the faster the battery charges.
  • Durability: Batteries can be susceptible to extreme temperatures, vibrations, shocks. Pick one suited to your usage.
  • Shelf life: The ideal shelf life for a deep cycle battery is 10 years before it loses maximum capacity.
  • Charging method: Note how the battery is charged. You can often use a Smart charger to help adjust voltage and current.
  • Temperature tolerance: Check its ability to deliver power at different temperatures, especially if you live in very hot or extremely cold climates.

How to Tell If a Deep Cycle Battery Is Bad

When your deep cycle battery won’t fully charge or charge at all, the battery is experiencing failure.

Other symptoms of a “bad” deep cycle battery include when the battery:

Shows sluggish performance

Experiences shorter run times

But why do deep cycle batteries go bad?

They’ve Reached Their Age Limit

For starters, deep cycle batteries have an age limit.

Forklift batteries, for example, usually last about 1,500 cycles.

And after this point, they begin to fail.

They’re Too Sulfated

Sometimes, deep cycle batteries can fail even sooner than their expected lifespan.

Most often, this happens because of a chemical issue called “sulfation.”

Sulfation is the formation and build-up of lead sulfate crystals on the surface of the battery’s lead plates.

Often, sulfation occurs when the battery is deprived of a full charge.

When this happens, sulfation reduces the surface area of chemical reactions.

And this causes the loss of plate capacity, which reduces battery performance.

Overall, most premature deep cycle battery failures are due to sulfation.

They Have Dead Cells

Dead battery cells occur when the plates shed active material.

This is due to expansion and contraction in the battery during its normal charge and discharge cycles.

When the material sheds, it causes a loss of plate capacity.

And this results in a buildup of sediment in the bottom of the cell, called sludge (or “mud”).

When this happens, these cells can short out the plates and end up “killing” the entire battery.

They Have a Short Circuit

Not just bad cells, but loose terminals can also cause short circuits.

Shorts produce a lot of heat as the current is instantly released.

If the battery short circuits, there will be evidence of burning or melting on the battery.

They Have Damage to the Case, Terminals, or Cell Connectors

Damage to batteries can result from several things.

For example, you can see evidence of excessive corrosion on this forklift battery:

If bad enough, this damage will cause the battery to go bad.

When Is a Deep Cycle Battery Considered “Dead”?

A deep cycle battery is considered “dead” when the active material in the plates can no longer sustain a discharge current.

Of course, you can’t tell this just by looking at it.

So, how do you tell when a battery is dead?

You’ll be able to tell if the battery drains quickly or cannot charge at all.

But you can also know when a battery is dead by checking its voltage.

Typically, the voltage of a fully charged, 12-volt deep cycle battery is between 12.8V and 13V.

But a dead battery’s voltage is below 10 volts.

How to Test a Bad Deep Cycle Battery

It is vital to detect battery problems at an early stage to resolve them.

You can only tell if a battery is bad or good if you inspect the battery regularly and test it if need be.

The three methods to test a deep cycle battery are:

To get started, you’ll need the right deep cycle battery test equipment.

This includes a voltmeter, hydrometer, and battery charger.

Once you have the right equipment, follow the steps below to test your battery:

Safety First!

Before handling lead-acid batteries, you need to take precautions against hazards like corrosion, flammable and explosive hydrogen gas, electric shocks, and burns.

  • Use proper personal protective equipment (PPE) including an apron, goggles, face shields, rubber gloves, and safety footwear
  • Work in an open or well-ventilated area
  • Remove metal jewelry, avoid smoking, and eliminate any other ignition sources

Step 1: Visual Inspection

Testing starts from the outside and moves to the inside.

So, here’s what to do during the visual inspection:

Look for Damage

Look for cracks or bulges in the case, broken terminals, excessive corrosion, broken cell connectors, and excessive leaks.

If found, remove the battery from service immediately.

Then, contact a battery professional to schedule repairs.

Note: AGM and gel batteries are designed not to leak, even if the case is damaged. But flooded lead-acid batteries will leak. Here’s the full Gel vs. Lead-acid battery comparison.

Look for Dirt and Debris

Check the top of the battery and the terminals for dirt and grime.

If you don’t, they can cause the battery to self-discharge.

And this can greatly reduce battery life.

The next two visual inspections only apply to flooded lead-acid batteries because you cannot open sealed (AGM and gel) batteries.

Check That There’s Adequate Water in the Cells

Check the battery‘s electrolyte level and make sure it covers the battery plates.

If the electrolyte is low, top up with water.

When in use, batteries only consume water. not sulfuric acid.

And if the electrolyte is low, it will self-discharge at a high rate.

This, in turn, will cause premature battery aging and possibly failure.

Check the Color of the Water Inside the Cell

The water shouldn’t be dirty or discolored.

If it is, there’s a problem with the cell.

And if one cell is compromised, the whole battery is compromised.

Check the Specific Gravity Readings

Specific gravity is the electrolyte’s weight compared to the weight of an equal volume of water.

Because it tells you the electrolyte’s strength.

And a properly mixed electrolyte is key to the proper functioning of the battery.

The specific gravity in a fully charged battery cell should be between 1.280 and 1.300.

If the specific gravity is off (over 10 points below or above), you’ll need to adjust the electrolyte.

So, how do you check the specific gravity?

First, you’ll need a hydrometer.

Then, using the hydrometer, remove some of the electrolytes and add water to lower the gravity if it is high.

If the gravity is low, you’ll need to add acid.

But because adding acid can be a dangerous activity, we recommend you contact a qualified battery technician to do this.

You can learn more about specific gravity and how to measure it in our Forklift Battery Maintenance Guide.

Step 2: Check the Voltage

Checking battery voltage can help to give you a clue into the health of the battery.

The voltage after a full charge will reveal internal battery issues like:

Before testing the voltage, you’ll want to complete a full charge.

IMPORTANT: Actual Voltages Aren’t as They’re Advertised

Each cell in a battery (just after a full charge) is 2.2 volts.

After resting for 12 to 24 hours, the voltage drops to 2.1 volts per cell.

So, a charged but rested 12-volt battery will actually be around 12.6 volts after charge.

And a 6-volt battery will read 6.4 volts.

It’s important to understand this, so you don’t get a false reading.

Then, you’ll need to remove the surface charge.

What Does Surface Charge Mean?

Surface charge is the extra voltage in lead-acid batteries that occurs because of the delay in converting lead sulfate to lead and lead dioxide after charging.

Why should you remove the surface charge?

A lead-acid battery with a surface charge has a higher voltage.

Thus, this can give a false voltage based on the battery’s state of charge (SoC) reading.

Now, surface charge is not a symptom of a battery defect.

It’s actually a reversible situation.

So, How Do You Remove Surface Charge?

One way is to briefly place an electrical load on the battery. such as turning on any lights connected to the battery.

This will remove about 1% of the battery’s capacity.

deep, cycle, battery, minimum, voltage

Alternatively, you can allow the battery to rest for a few hours after charge before taking a volt reading.

Measure the Voltage

Once you’ve removed the surface charge, you’ll want to read the voltage to determine the state of charge.

You can do this with a multimeter.

The multimeter indicates the voltage with a solid and a dashed line above the letter “V.”

For example, here’s how to test a 12-volt deep cycle battery with a multimeter:

Set the multimeter dial to 20. This will allow you to measure the battery between 0 and 20 volts accurately

Now, touch the meter’s red probe to the positive terminal and the black probe to the battery’s negative terminal. The battery’s terminals are marked “” and “-”. And they’re usually color-coded with red for positive and black for negative

Notice that if you’re getting a reading with a minus in front (e.g12.6 instead of 12.6), it means you’ve placed the probes the wrong way around! Change them and read them again

Correlate the Voltage to the State of Charge

Once you have the voltage, you’ll want to correlate that with the battery’s state of charge.

The state of charge (in %) to voltage reading should be as indicated in this 12-volt deep cycle battery charge chart:

Discharged: 0 to 11.9 volts

This will tell you your battery’s health level.

For example, if your battery is:

0 volts. it indicates a short circuit

Below 10.5 volts. it indicates a dead cell(s)

Below 12.4 volts, but charger indicates it’s 100%. the battery is sulfated

What Should a 12-Volt Battery Read When Fully Charged?

As we’ve discussed, the battery’s ideal resting voltage should be no lower than 12.6V.

If it goes down to 12.2V, then it’s only 50% charged.

And if it’s below 12V, that means the battery is discharged.

Step 3: Perform a Load Test

Load testing batteries involves measuring the actual capacity of a battery under an electrical load.

This test essentially shows you how well your battery will perform under normal conditions.

Where Can You Load Test Batteries?

For consumer-use batteries (6-volt, 12-volt), you can buy and use a deep cycle battery load tester.

For larger industrial batteries (like forklift batteries), you’ll need an industrial load tester.

But these are prohibitively expensive.

So, you’ll need to contact a battery service center (like Foxtron) for this service.

How to Load Test a Deep Cycle Battery Using a Load Tester

This is the general process for conducting a load test:

Measure and record the specific gravity of each cell (do not start the test unless specific gravity is below 1.280)

The test is complete when either a cell’s voltage drops significantly or when no battery cell drops below 1.70 volts within 6 hours

How to Tell If a Battery Is Bad from a Load Test

Once the load test is complete, you can estimate the capacity of the battery as follows:

  • 1st hour complete: 60%
  • 2nd hour complete: 70%
  • 3rd hour complete: 80%
  • 4th hour complete: 90%
  • 5th hour complete: 100%

If a battery cell’s voltage drops significantly during the test, that indicates that the cell is bad and should be replaced.

What Should You Do If Your Battery Failed the Load Test?

First, load test it again to confirm.

And if it still fails, it’s time to repair or replace the battery.

Can a Bad Battery Test Good?

Batteries with open cells can read fully charged in idle but may fail under a load test.

You need to conduct a load test and the other inspections we’ve mentioned here to check if the battery is good or bad.

How to Bring a Deep Cycle Battery Back from the Dead

Whether or not you can resurrect a dead deep cycle battery depends on the condition it’s in.

If the battery is damaged, you should discard it.

If the battery has suffered a dead cell, you can replace the cell.

But this can be very expensive.

So it may make more sense to simply replace the entire battery.

If the battery is dead due to sulfation, resurrecting it depends on whether the sulfation is permanent or reversible.

If it’s reversible sulfation, a typical equalization charge (overcharge) will help bring the battery back to life.

But if the battery is fully discharged, you can’t charge it with a Smart charger (i.e., a charger that automatically detects charge state).

The charger won’t read enough of a voltage from the battery to start the charging process.

Charge it using a non-Smart, manual charger to deliver voltage without detecting the battery’s state of charge.

If you can’t do this, you can contact a professional technician or seek the services of a professional battery company like Foxtron.

Tips for Maintaining a Deep Cycle Battery

Fortunately, many of the issues that cause deep cycle batteries to go bad are preventable.

It mostly comes down to keeping up on maintenance.

Conduct a capacity check for new batteries as part of acceptance to avoid buying low-performance batteries

Allow the battery to have a full charge of between 14 and 16 hours regularly

Charge in a well-ventilated area to prevent the accumulation of hydrogen gas

Inspect the battery regularly to note and repair any issues like damage and leakage

Water regularly to prevent sulfation and stratification. Don’t allow the electrolyte to drop below the plate-top levels. Exposed plates will sulfate and reduce the surface area for chemical reactions

When watering the battery, add only distilled or deionized water until it covers the exposed plates before charging

Never add acid to the electrolyte. This can raise the specific gravity and cause excessive corrosion. If acid needs to be added, contact a battery professional

Keep the battery charged, especially when not in use, to prevent self-discharge. Avoid storing the battery below 2.07 volts per cell or when the specific gravity level is below 1.190

Avoid deep discharges. Deeper discharges shorten the battery life. You can conduct a quick charge of 1 to 2 hours to prolong battery life

Keep the battery clean to prevent the accumulation of dirt that can interfere with the performance

Format a new deep cycle battery by applying gentle load for the first five charge cycles to gradually increase performance


There you have it: How to tell if a deep cycle battery is bad or not.

Now, we’d like to hear from you.

Can you tell whether a deep cycle battery is bad or not?

Share with us in the Комментарии и мнения владельцев section below!

How should a deep cycle gel battery used for a back up sump pump be maintained? Should it be allowed to have some discharge cycle or kept at full charge with a maintaining charger. I would expect limited use except for infrequent extended power outages.

Using a maintenance charger would be the best option, but it’s not absolutely required. Most gel batteries discharge only a small percentage of their total capacity each month, and can safely discharge to around 70-75% (check with the battery manufacturer to be sure). It’s a good idea to check on the battery at least every 3 to 6 months and give it a charge back to 100% if needed. I’ve included a couple links to articles that explain a bit more about deep cycle battery discharging and storage best practices:

Thanks for reaching out and I hope this helps — cheers!

Battery after full charge rests at 12.7 but when load tested shows to be mid week is this normal?

If the battery is at 12.7 volts resting after charge, but then it drops significantly under a load test, it probably means that the battery isn’t working properly. Or the capacity has diminished. To know for sure, you’d have to conduct more extensive testing. Feel free to drop us a line with more details about your battery. We can help point you in the right direction. Cheers!

Hi, I have a deep cycle battery that is about 12 years old and hasn’t been charged in 5-10 years. It shows a few volts. I have tried both a marine battery charger with ‘manual’ position and a standard auto battery charger. Both peg the amp-meter on the charger then the breaker trips, resets after a few minutes, then the cycle repeats. I’ve left on for an hour or so and it takes a little charge but the voltage drifts down after removing the charger. Any hope for the battery or is it a lost cause? It’s an Interstate Deep-cycle Extreme 232 AH, I assume lead-acid type. Thanks for any help!

Thanks for reaching out. I think you might have a hard time resurrecting that battery if it hasn’t been charged in 5-10 years. At this point, it’s probably permanently sulfated and unlikely to come back. You’re probably better off dropping it off for a core charge and getting a newer battery. If you want to learn more about sulfation and its effects on batteries, check out our article here: What Is a Sulfated Battery? Tips for Prevention and Restoration

Hello. I bought a new battery 2 weeks ago. I had to top charge it before I could use it. It had an 80% charge then. 2 days later I took it out and it arched when I was going to the lake. The battery looked fine, only a few burn marks on the batter. Boat bench took the worst of it. I’m worried I burnt a cell up. I put it on 2A white charging it. I took it off the charger when it was full and let the surface charge wear off. When I took it off, the voltmeter read 12.65 volts. After 6 hours it reads 12.56 volts. And after 24 it reads 12.53. 48 hrs 12.52 Did I damage it, or in this normal. For a new battery?

Based on the information you provided, it’s possible that the arcing was caused by damage to the battery, which may have resulted in contact between the positive and negative electrodes. You said that you see some burn marks on the battery case. It’s possible that the internal components may also have been damaged. You may want to have the battery inspected by a qualified professional to ensure that it is safe to use — especially given the potential safety concerns related to the arcing and shorting.

Regarding the voltage readings you provided, if they were taken without a load on the battery, they may not accurately reflect the battery’s actual state of charge or capacity. However, if the readings were taken with no load, the gradual decrease in voltage over time looks normal (though perhaps a little low) for a lead-acid battery that is not being used or recharged during that time.

To get a more accurate idea of the battery’s performance, it may be helpful to put a load on the battery. Then check the voltage at regular intervals to see how well it is performing. You may want to consult the manufacturer’s instructions or specifications to see what the expected voltage range is under a load. For example, here’s one such chart:

Again, if you have concerns about the battery’s condition or performance, it’s always a good idea to have it inspected by a qualified professional. They can see if there is any underlying damage that could pose a safety risk. Thank you for reaching out and good luck!

I purchased a 42-volt street legal golf cart 6 months ago and drove it 15 miles to home. It would work for 18 holes and more until recently. Now it dies after only a few miles. I checked the voltages. 6 of the 7 batteries read 6.1-volts however the 7th read 4.2-volts. The last time I charged the batteries, the charger got very warm and did not work right so I did not complete the charge. In addtion the detection Fault light turned on but subsequently went off, Will one bad cell cause the cart to die after a short usage. Was the Detection Fault light on due to the bad cell. If I replace only the 7th battery with the bad cell; will that solve the problem? Thanks for your help.

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