Deep Cycle Battery FAQ. Agm solar battery bank

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.

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.

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 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.

deep, cycle, battery, solar, bank

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

Guide to Solar Batteries: Are They Worth It? (June 2023)

Check out this guide to see how solar batteries can complement your solar system and learn about the cost, types of batteries and more.

Leonardo David is an electromechanical engineer, MBA, energy consultant and technical writer. His energy-efficiency and solar consulting experience covers sectors including banking, textile manufacturing, plastics processing, pharmaceutics, education, food processing, real estate and retail. He has also been writing articles about energy and engineering topics since 2015.

Tori Addison is an editor who has worked in the digital marketing industry for over five years. Her experience includes communications and marketing work in the nonprofit, governmental and academic sectors. A journalist by trade, she started her career covering politics and news in New York’s Hudson Valley. Her work included coverage of local and state budgets, federal financial regulations and health care legislation.

Solar panels can save you thousands of dollars in electric bills during their lifespan, but your panels will only generate power during daylight hours. Solar batteries remove this limitation, providing an energy storage system you can count on during cloudy days and nighttime.

Stand-alone solar panels are an excellent investment, but a battery bank improves their functionality. In this article, we at the Guides Home Team will cover everything you need to know about solar batteries, including different types and how they work, the cost and how to choose a battery for your solar system.

  • What Are Solar Batteries?
  • Battery Costs
  • Types of Solar Batteries
  • How To Choose Solar Batteries
  • The Bottom Line

Offers a range of financing options 24/7 customer service line Panel insurance protects against theft and damage

Packages include 24/7 system monitoring 25-year warranty guarantees power production, product performance and workmanship Installation process is handled 100% in-house

What Are Solar Batteries?

It’s important to note that the rated power of solar panels and battery storage systems are not the same. For example, you could have a 10 kW home solar system with a battery that has a rated power of 5 kW and 12 kWh storage bank.

How Much Do Solar Batteries Cost?

You can expect to pay around 25,000 to 35,000 for a solar system and battery, depending on the size and other factors like your location, according to the U.S. Office of Energy Efficiency Renewable Energy. It is typically cheaper (and easier) to install both your panels and battery at the same time — a battery alone can cost around 12,000 to 22,000 if you decide to purchase storage after you install solar panels.

In terms of performance, lithium-ion batteries are considered the best option for home applications where you need daily charging and discharging.

  • The latest lithium-ion batteries offer a lifespan of over 4,000 cycles, meaning they can last over 10 years with a daily charging cycle.
  • The price of lithium-ion batteries varies depending on the brand and energy storage capacity, but most homeowners can expect to pay around 10,000 to 15,000 for a battery system (without solar panels).

Thanks to the Inflation Reduction Act, which was passed in August 2022, solar batteries qualify for a 30% federal tax credit. This is a credit you can claim on your federal income taxes for the year you purchase your solar system. So for example, you can claim 3,000 as a tax deduction if you purchase a 10,000 unit. While you can only claim the credit once, you can roll it over to the next year if the taxes you owe are less than your credit amount.

The table below outlines the key features of four common types of solar batteries, along with the average cost of each when used in residential settings.

Solar Battery TypeSizePowerCost Range

The National Renewable Energy Laboratory (NREL) publishes periodic reports with the latest cost data for solar and battery systems in residential, commercial and grid-scale projects. The Pacific Northwest National Laboratory (PNNL) keeps a similar database, which covers multiple battery technologies in megawatt-scale applications (larger than 1,000 kW).

Types of Solar Batteries

All solar batteries have the same basic function, but each type is suited for different applications. Your solar battery will offer higher reliability and return on investment when its chemistry is suitable for the application at hand.

For example, some electricity consumers are subject to higher kWh at certain times of the day, or additional charges for sudden peaks in consumption. In this case, you need a battery bank capable of delivering large amounts of electricity in a short time. Lithium-ion batteries are suitable for this task, but not redox flow batteries.

Regardless of the battery type, you also need to consider the depth of discharge (DoD), which indicates a battery’s usable capacity. The service life of a battery can be drastically shortened if you exceed the DoD, or you can even cause permanent damage. For example, using 70% of the stored energy is acceptable with a solar battery rated for 80% DoD, but not a 50% DoD battery.


Lead-acid batteries are an established technology, commonly used by off-grid solar energy systems in remote locations. Lead-acid batteries are affordable and have a well-established supply chain due to their popularity, so you can easily find vendors and technical support.

In spite of their low cost, lead-acid batteries have some technical limitations you should consider:

  • Lead-acid batteries typically have a charging life of 500 to 1000 cycles.
  • Batteries should be fully recharged after each use, or the lifespan is drastically reduced.

An absorbed glass mat or AGM battery is an improved version of the traditional lead-acid battery. They can charge faster while having a spill-proof design and more durability. You can also find AGM deep cycle batteries that are designed for 80% DoD.

Using lead-acid batteries along with solar panels requires charge controllers to sustain a suitable charging current. These batteries should not be wired directly to your solar array, or your system may be damaged by excessive current.


Lithium-ion batteries have become very popular in recent years since they can achieve synergy with solar panels and wind turbines. For example, the Tesla Powerwall and Enphase IQ are two types of lithium-ion batteries commonly used in home solar applications. You can also find smaller lithium batteries from brands like Renogy and WindyNation, which are portable and better suited for DIY solar projects.

Lithium iron phosphate or LFP batteries are a subtype of lithium batteries, characterized by a superior service life. The best LFP batteries offer a service life of over 4,000 cycles at 80% DoD, which means they can last for over 10 years on a daily charging cycle. This makes LFP batteries the ideal complement to solar installations. Unlike lead-acid batteries, which need separate charge controllers, many of the lithium battery models that are commercially available come with built-in chargers and controls.

The main drawback of lithium-ion batteries is the high price, but this could change in the near future — the U.S. Department of Energy is targeting a 90% energy storage cost reduction by 2030. Lithium batteries can also suffer a phenomenon called thermal runaway when used at high temperatures, which causes them to catch fire. You can prevent thermal runaway by making sure your batteries are high-quality and installed by qualified electricians.


Nickel-cadmium batteries are characterized by their durability, tolerance to high temperatures and simple maintenance needs. Thanks to these performance features, nickel-cadmium batteries are popular in industrial and utility applications. Unfortunately, cadmium is highly toxic to humans, so nickel-cadmium batteries are not recommended in homes.


Flow batteries store energy by separating positive and negative electrical charges in chemical solutions, which are stored in separate tanks. When these two solutions interact, they undergo a reduction-oxidation reaction (redox) and the battery releases energy. This battery technology is also referred to as “redox flow” for this reason.

The main disadvantage of redox flow batteries is their space requirement, and they are not cost-effective for small-scale projects. Even a small redox flow battery system can be the size of a shipping container, so using flow batteries in home solar systems is not viable.

How To Choose a Solar Battery

The first step to choosing a solar battery is to understand your energy needs. The average annual electricity consumption for a U.S. resident was 10,632 kWh in 2021, which averages out to around 886 kWh per month, according to the U.S. Energy Information Administration. Knowing your average energy consumption can help you better determine important factors like your ideal battery capacity, or how much energy a battery can store.

Lithium-ion batteries are recommended for home solar systems since their long service life is suitable for a daily charge cycle. However, lead-acid batteries are viable as backup power systems that are used occasionally, or as part of an off-grid system.

Home batteries can be classified based on how they interact with solar panels:

  • Direct current or DC-coupled batteries use the same inverter as your solar panels, and both systems are connected to the DC side.
  • Alternating current or AC-coupled batteries have a separate inverter, which connects directly to your home’s AC wiring.

You can only use DC-coupled batteries if you have a hybrid inverter, which is designed to manage solar panels and energy storage simultaneously. If your solar panels have a traditional inverter that cannot handle energy storage, you need an AC-coupled battery with a dedicated inverter.

If you intend to use your battery as a backup power source, check its specifications to make sure it can operate off-grid. Not all solar batteries are designed to be used during power outages, and many models can only operate when synchronized with the grid.

The Bottom Line: Is a Solar Battery Worth It?

In general, installing a solar battery is worth it when you can achieve higher savings than the cost of ownership. A home battery can add over 10,000 to the cost of a solar panel system. but there are several scenarios in which you can take advantage of energy storage, including:

  • You can avoid the highest kWh on a time-of-use tariff, or when the price of electricity changes depending on the time of day
  • You can reduce energy demand charges (if included in your electricity costs)
deep, cycle, battery, solar, bank

You cannot use solar panels alone as a backup power source during blackouts or suboptimal conditions, due to their variable output, but a charged battery can keep your appliances running. Plus, if the local electric company charges higher rates during certain hours, you can avoid costs by switching to a solar battery.

A solar battery is also useful if your local power company does not offer net metering. While you won’t get credit for sending excess solar power to the grid. a battery will still let you use that extra energy. However, this only makes financial sense if the cost of battery ownership is less than what you would pay to use the grid normally at night.

Keep in mind that the 30% federal tax credit is not only available for solar panels, but also for home batteries. This tax credit can be combined with any solar incentives offered by local governments and utility companies. The financial return offered by a solar battery system improves when you combine incentives from several programs.

How to Choose the Right Battery for your Solar System?

Solar Battery is useful, but not saving money every time.

The battery bank in a solar system is used to store energy for consumption at night or on rainy days. Sometimes, the battery bank can also be a backup power supply to keep the whole system running.

It depends on your actual demand and your desire.

Do you really need Solar Battery?

In general, there are three types of solar systems, on-grid, off-grid, and hybrid. The inverters used in these three types are different, so please pay attention to the differences.

On-Grid Solar System

When more power is generated than consumption, the excess power is fed directly into the grid. Oppositely, we get the power from the grid.

Theoretically, an on-grid solar system does not need any batteries.

Recently, Feed-in Tariffs (FIT) reduced. A lot of people choose to build their own battery banks for daily consumption to reduce electricity bills, which is a good choice.

But if your solar system is on-grid, and the FIT is good, it is not necessary to add a battery bank.

Off-Grid Solar System

Because of the isolation from the grid, the off-grid solar system is a small, independent system. All required energy must be from its own. So the battery bank should provide sufficient energy or a backup power source such as a generator will be required.

Since solar energy is highly affected by the weather and sunlight, wind and solar hybrid system is also a good option.

In an off-grid solar system, the battery bank is very important, even more important than the solar panel array.

Battery Bank is very important for an off-grid solar system.

Hybrid Solar System

Here hybrid solar system refers to on-grid and off-grid hybrid, not wind-solar hybrid.

The biggest advantage of a hybrid solar system is that if the grid fails, we will still have our own electricity to use.

Hybrid solar system is ideal for areas where the grid is not so stable. If the grid is uninterrupted and nearly perfect, then a battery backup system does not seem to be necessary.

Unless there are important devices that are not allowed to be off. It works similarly to a UPS system.

Commercial, Residential, and Vacation Cabin

Most commercial solar systems are on-grid because the energy is consumed at the same time as the energy is produced, which is during daylight hours.

For residential use, we usually choose solar to save money on electricity bills or go for clean energy for eco-friendly purposes.

In the first case, the solar system could be also called an “investment”. Depending on local weather conditions and policies, we will need to calculate how long it would take to pay back the cost of the whole solar system. After that, all the earnings are benefits.

If it’s the second, it’s all about how much you can afford, and how much you want to take. I know a number of friends who enjoy a renewable energy system purely for its own sake.

If it’s for a vacation cabin, and it is far away from the grid. As a small off-grid system, a battery bank is necessary.

Considering the fact that we only go there on vacations, no time for maintenance, and low frequency of use, Deep Cycle AGM batteries (A type of Sealed Lead Acid Battery) are probably the most preferred option.

Would you like to spend time on your Solar Battery?

The most traditional battery-flooded lead-acid batteries require regular maintenance and additional water. It needs maximum maintenance.

It means we need to spend a lot of time and effort, but of course, outsourcing to a professional is a good option.

VRLA Deep Cycle batteries will work for 3-5 years, and require voltage and damage checks. Only a few time will be required, much less than flooded batteries.

With a lower budget, deep-cycle AGM battery is recommended.

LFP (LiFePO4) batteries could save a lot of time and effort, it will enable you to concentrate more on your career and family.

LiFePO4 is the safest option in lithium technology. With a much better cycle life, it is widely used in a huge range of applications. Especially, the “blade battery” developed by BYD, can withstand pinprick tests without burning.

There are some integrated solutions from famous brands such as TESLA, the battery can be used as a common household appliance, requiring no maintenance. It is a beautiful, wall-mounted type that requires very little room. The only thing is, it is still expensive.

Alternatively, we have also developed our Residential Powerwall, cost-effective, and compatible with most of the inverters in the market.

For home energy storage, there are also Residential Stack Cubes, ES Box, and Rack-Mounted Modular batteries.

Relatively, a lower-cost solution is the 12V, 24V MonoBlock LiFePO4 battery, designed as a drop-in replacement for VRLA battery. It is a very nice alternative to the original lead-acid battery replacement.

Options for Different Scenarios

MonoBlock LiFePO4 Battery for 12/24V System

The most cost-effective battery in the long term, expected to work for 10 years or more.

Drop-in replacement for lead acid batteries.

Renowned All-in-One Solution

No maintenance, good-looking, only expensive.

Residential Powerwall

No maintenance, data monitoring, communication function, cost-effective.

Residential Stack Cubes

Stackable, Less space, Higher Energy. Also offers an option of inverter integrated.

Server Rack Modular LiFePO4 Battery

Fit in 2U, 4U standard rack systems, scalable.

Deep Cycle AGM/Gel Battery

Still, for a lot of families, deep cycle AGM/Gel battery is stable and affordable.

Off-Grid Solar Project

Here we are referring to projects with large energy storage demand, such as 96V, 110V, 220V, higher voltages, and capacities of 1000Ah, 5000Ah, 10,000Ah, and more. (MWh)

Options for different electricity consumption

The following is just for example, one cycle per day, without considering rainy days and other conditions.

Typical household Monthly 300kWh

Equals to around 10 kWh per day, Residential Powerwall 10kWh (51.2V200Ah), or LFP12V200Ah4, or Deep Cycle AGM 12V200Ah8 (50% DOD) are recommended.

Except for the wall-mounted type, all require a small battery rack with a space of about 0.5m0.5m.

Monthly 150 kWh

Equals to 5 kWh per day, Residential Powerwall 5kWh, or LFP 12V200Ah2, or Deep Cycle AGM 12V200Ah4.

Monthly 600 kWh

In short, double as 300 kWh.

2 units of Residential Powerwall 10kWh.

Vacation Cabin for light or charge only

One battery of 12V200Ah, could be good enough.

Or 24V100Ah, 24V200Ah for occasional use.

Advantages and Disadvantages of different types of Solar Battery

Cost Lifetime DOD Labor
Deep Cycle AGM Battery
Tesla Powerwall ☆☆☆☆☆☆ ☆☆☆☆ ☆☆
MonoBlock LiFePO4 Battery ☆☆☆ ☆☆☆ ☆☆
Residential Powerwall ☆☆☆☆ ☆☆☆☆ ☆☆
Flooded Lead Acid Battery ☆☆ ☆☆☆

Sealed Lead Acid Battery (Deep Cycle AGM Battery)

With reasonable and stable performance, deep cycle AGM battery is still a choice for a lot of customers.

The shortage is, for the developing economy, its cycle life is not as good as LiFePO4 battery.

Tesla Powerwall

Good-looking, only expensive.

MonoBlock LiFePO4 Battery (12V LFP)

MonoBlock LiFePO4 Battery is a type of LiFePO4 battery using Lithium Iron Phosphate technology, considered to be the safest li-ion battery.

LiFePO4 is more chemically stable, and it is incombustible, which means that it is not prone to thermal runaway, and remains cool at room temperature. It can also withstand high temperatures without decomposing, and it is not flammable.

Residential Powerwall

Residential Powerwall is now the most popular, with long lifespan and no maintenance.

With the BMS protection from all aspects, and the monitoring and communication function, it is considered as the safest, and longest lifespan option.

Flooded Lead Acid Battery

Best cost-worthy, but it takes too much maintenance.


If it’s about saving money, in the long run, saving effort, saving time, MonoBLock LiFePO4 battery and Residential Powerwall is definitely the best choice. Of course, it may be over your budget, then AGM deep cycle battery is also good, only the lifetime will be relatively short, 3-5 years to replace.

Flooded Lead Acid Battery is probably the first choice for professionals, regardless of maintenance expenses, the relative cost is the lowest.

Thank you for reading, I hope it helps. If you have any questions, please leave your Комментарии и мнения владельцев below.

Hi, I’m Andy. Since the year 2015, I’ve been working in SunOn Battery, a manufacturer in China that makes various batteries for 15 years now. The purpose of this article is to share with you the knowledge related to batteries and energy storage solutions from a Chinese supplier’s perspective.

RV Solar Power Kits and AGM Batteries

A full selection of complete RV solar power systems with AGM batteries for the house battery bank.

Complete power kits for your RV include an Inverter Charger, solar array for charging your RVs house battery bank. In this group of products, we include AGM batteries. These Absorbed Glass Mat (AGM) batteries are second to only the lithium kits. AGM batteries can be more affordable, but they do require larger banks and more weight. The warranty on AGM batteries is also much less than their lithium counterparts.

Inverter Chargers for easy power

Go Power IC-3000 Inverter Charger Inverter chargers like the IC-3000 pictured include several components in one unit. A true sine wave power inverter, a transfer switch, and a battery charger. With these three items in one unit, there is greater control over the entire inverter and battery charging system.

We carry Inverter Chargers in both 2000 and 3000 watt configurations.

Larger solar arrays

Newer RVs require larger arrays to power the items on board. Everything from TVs to residential refrigerators are power hungry devices. These devices will drain your battery bank, but a good solar array can work to create a charging balance.

This is a great entry levelf Go Power’s Inverter Charger Kit. They offer the Elite and Extreme kits. These have different amounts of solar and also different size Inverter units.

The Go Power! Elite Solar Kit. IC-2000. 380 Watts of solar

We have found these kits contain much of what you need for getting going with off-grid solar and inverter power. We have also added lithium battery and sealant as well

As an Amazon Associate I earn from qualifying purchases.

Materials and content on this site are provided “as is” and “as available” without warranty, guarantee, or representation. Content is informational only. By accessing this site, the user assumes all risk and responsibility related to any materials used or relied upon by the user and understands that all claims against Outside Supply, LLC are waived and, furthermore, that Outside Supply, LLC disclaims any and all warranties, representations or guarantees as to the materials available on this site.

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