Alternative Energy Battery Type 101


Many of the batteries used in alternative-energy ‘off-grid’ solar powered systems are Lead-Acid type batteries. Even after over a century of use, they still offer the best price to power ratio.

ALL of the batteries commonly used in deep cycle applications are Lead-Acid. This includes the standard flooded (wet) batteries, gelled batteries, and AGM (Absorbed Glass Mat) batteries. They all use the same chemistry, although the actual construction of the plates, etc., varies.

Here’s more information about some of the different types of batteries, and a request for your input regarding what you may be using yourself…

(Updated and re-posted)

Expected Battery Life

These are some typical expectations for battery life if used in deep cycle service.

Note: ‘Deep Cycle’ is discharging a battery down to apprx 20% (80% discharge).
Note: Battery life will increase if only discharged down to 50% (a common design goal).

Starting battery: 3-12 months
Marine battery: 1-6 years
Golf cart battery: 2-7 years
Gelled deep cycle battery: 2-5 years
AGM deep cycle battery: 4-7 years


Starting 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 an be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.

Golf cart batteries are quite popular for small systems and RV’s. The problem is that “golf cart” 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, Deka, 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. 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.

Gelled deep cycle 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 (must be charged at a slower rate and lower voltage to prevent permanent damage, In hot climates, water loss can be enough over 2-4 years to cause premature battery failure).

AGM, or Absorbed Glass Mat deep cycle batteries have all the advantages (and then some) of gelled, with none of the disadvantages, and they can take much more abuse. Since all the 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. AGM’s will cost 2 to 3 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.


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.

Although some batteries are designed to be able to deep cycle down to 20% (80% discharge), a good guideline is to limit discharge to 50% (or less) to prolong its usable life.

If batteries will be kept indoors, either you will need a special designed (and vented to the outside) battery box (hydrogen gas), or you will need AGM batteries (sealed and safe).

I have some experience with the Lead Acid Trojan T105 (6 volt, 200AH) golf cart batteries, and they’ve been a ‘work horse’ on a previously installed solar panel system. I believe they’re one of the best values going – probably due to high volume production for golf carts, etc..

I am currently running with 16 Trojan AGM-31 batteries (12 volt, 110AH each, wired in a 48-volt configuration). Reason being… my battery bank is kept indoors (AGM type required), and I can handle them at 70 pounds each whereas other larger batteries are hundreds of pounds. I chose to keep them indoors because I live in a cold weather climate during the winter. Batteries perform very poorly when they’re cold (e.g. if they were outside in a battery shed). So I ‘bit the bullet’ and paid the higher price for AGM’s, while also choosing not to build a special designed battery room for lead-acid vented batteries.

I’m curious to hear your experiences and opinions, or which batteries that you are using on your alt-energy system…


  1. I also use Trojan T105s for about five years, they were factory reconditioned for $89.00 a piece. That was a great deal for those batteries I feel. Both battery banks are now using Powertrons about same price new but I’m not sure they have the capacity of the Trojans cannot find any detailed info on them.

    Outback Flexmax 80 controller
    Morningstar 30 amp controller
    8 Solar Cynergy 12v 110w poly panels
    4 Solar Cynergy 100w mono panels (seem to make the most power)
    6 Unisolar 100w thin film panels
    Two aeperate systems Two seperate inverters
    2200w pure sine
    10,000w 20,000 surge Modified /square wave
    Midnite solar DC disconnect
    so on …

    I appreciate your articles.
    Solar is probably one of the better things I have ever done.There is no electric bill here, no not so smart meter, no tax on it, no surcharges on it, no meter fee. It’s paid for and has given me a better return than my silver for six years running. Completely off grid.

    Thanks Ken

  2. The first set of factory rebuilt Trojans were really worked hard and much to my chagrin were even run with the acid below the top of the plates at least 4 times ….AHHHH.

    That is a great testament to them.

    The Powertrons are probably made in china, although they seem OK for about two years now. Bought them at golf cart shops and they all say they are just as good and the same in capacity but there is no info from them or online that I can find.

    I loved building the system and working with it still to this day.

    People looking into Solar should get a good controller with as much capacity on amps as possible like the Flexmax 80 just love it .

    Inverter surge time is very important to start any kind of motor (like wash machine,compressor). Most motors do not like square or modified sine wave inverters. If I chose one inverter, it would be a pure sine wave 2500 watt 5000 surge or larger.

    Along with Batteries The right size or larger cables from batteries to inverter…and controller to disconnect. I’m sure this blog has had that posted somewhere. I’m new to the site and have not got around in it much… ……….yet.

    Good talking to you, Good day to all.

    1. I can attest to the quality of the Outback Flexmax 80 charge controller and the Outback VFX 3648 sine wave inverter (have them both). I agree that it’s important to use a pure sine wave inverter rather than the cheaper modified square wave inverters.

      I plan to do more posts on solar powered systems in the future. I have a few posts on the site already, but do plan to relay more information going forward…

      1. Ken why pure sine wave. I have been using a Trace 12 volt modified sine wave for over 20 years on an off grid system. It seems to work just fine. Back then that was the best they had and 12 volt was all there was. Still going. No computer built into it no problems.

        1. A pure sine wave (also known as a true sine wave) inverter will less likely damage electronics equipment due to a number of technical factors. While apparently a modified sine wave inverter will work okay with many electronics, and they do cost much less, I chose not to take the chance here since I am somewhat heavily invested in electronic gear.

        2. Motors can also have problems with modified sine wave. Having your refrigerator or freezer motor die due to bad power probably won’t be considered a win. Certainly not in the middle of Summer.

          Pure sine wave inverters are more expensive. Maybe get a line conditioner to smooth out the power?

  3. One more thing on the batteries…
    Wiping up any excess water off the tops of the batteries after filling and coating all connections with a spray on anti corrosion spray is the cats meow.
    You do not have to coat everything with baking soda,not cleaning up or coating your battery terminals will end up looking like the you tube fire hazard solar builders OMG.The battery box used here is a Lowes deck storage box. It along with the batteries looks showroom condition after more than six or 8 years now.

  4. Running 8 big Trojan L16P-HC 428AH batteries in my 48V system. The system is headed up by an Outback FP-1 which has a 3600W inverter and an FM80 charge controller. I have 16 230W panels setup, and I’ve been able to wire my home 900sq/ft 2 story cottage in Central America much like what we had been accustomed to in the USA. We just made the move earlier this year, and we are very excited to be off grid :-)

  5. I did quite a lot of research deciding which batteries, etc. to choose. About two years ago I finally purchased two Rolls-Surrette S-600 450AH 6-volt batteries as the basis for my system. The manufacturer claims they can be discharged to 50% and recharged 1280 times. Rolls offers a higher grade battery series, but these were beyond my budget. The batteries are maintained by an IOTA Engineering “smart” charger, which periodically and automatically de-sulfates the batteries. They deliver power through a Samlex 2000 watt true sine inverter.

    Up to this point the system has only been minimally tested, but I hope to give it an extended load test soon.

    I also have some of the components for a solar charging system, but it is not operational yet due to subdivision and other concerns.

  6. My $.02 is buy the inexpensive marine deep cycle batteries available at Walmart. Never discharge them below 50% (12.06 volts) but try to keep the discharge closer to 20% (12.42 volts). The batteries will easily last 6 years maybe more. This will give you the best return on investment.

  7. Hey all! I too use the Trojan t105. just purchased second set t105RE’s, 16 of them, again. Last purchase was almost 8 years ago in march. For a 3648 outback solar system. they still have good life in them. Two banks of eight in series parallel. Yes 48 volt set up. Make sure you got the right generator, been using Coleman Pro-Gen 6500kw. However a Generac 5500kw will suffice. 6500 uses to much gas. Another look see would be wood gas conversion kit when gas is cut off to public. and Make sure you use super unleaded gas. ethanol is bad news for all engines. no regular unleaded. Corn is for feed/food not engines. Totally off grid. I’m satisfied with both Trojan Batteries and Outback Solar Systems. a word of advise, READ. I’m still learning, and half paralyezed. Now get prepared!!!! God Bless the Believers.

  8. I have completely solar powered my house for 3 years. My system is as follows:

    72 each Kyocera 300 watt panels
    4 each Xyntrex 80-600 charge controllers
    3 each Outback Radians 8000 watt
    32 each Rolls Surrette S605 405 am-hour batteries (48 volt system)
    various other system programing components and disconnects

    The performance was flawless for 2 years and then one of the Radians caught fire and was completely destroyed. I rebuilt that part of the system and it is again functional. The down side is that Outback completely washed their hands of the problem. I sent the inverter back to Outback for analysis and the company will not tell me why there was a fire in the inverter. If I were not an electrical design engineer(25 years experience) the fire would have really scared me out of the solar power system. For a non engineer trained type I think the fire would have been too much but over the years I have seen electrical fires before.
    My system is contained in a building separate from my house.

    1. @No joke, Out of curiosity, was the Inverter fire entirely contained within the Inverter itself? Did it burn outside of its ‘shell’ (was there a risk of catching fire to the wood that it was mounted to)?

      By the way (and I’ve mentioned it before) your system is incredibly impressive.

      My current system is very small in comparison, but is just enough to run all of the critical systems here at the house.

      (12) Solar World Pro XL 315 watt panels
      (1) Outback Inverter VFX3648 (3.6 kW)
      (1) Midnite Solar ‘Classic 200’ Charge Controller
      (16) Trojan AGM-31 batteries
      …and all the various combiners, breaker panels, disconnects, etc..

      1. @Ken
        How many AH is your battery bank?
        Im thinking along doing my house system along the same lines as your system because most of the hardware is readily available here on island from what i can see and the batteries are much much cheaper and also readily available locally.

  9. Ken,
    The fire was contained within the inverter housing itself and I do not think It would have spread outside to the building. The fire was mainly in the printed circuit boards located below the power transformers. The inverters are protected by 175 amp breakers but that certainly not protect the circuit boards. A good system design would have contained current limiters for the boards or a thermal sensor/cutout device.

    1. Maybe you should contact underwriters laboratory? Aren’t they the ones who determine electrical product safety?

      1. To get a UL listing, I think you pretty much have to prove the equipment works (somewhat) as advertised. I’ve seen some real garbage with UL listings.

        Just like patents and licensing, UL listings are designed to protect the big guys from competition.

        1. UL certification used to mean that a product was ‘safe’. Not that it worked as intended. UL is now a for profit concern and kind of a joke. The requirement for UL certification does still get into contracts.

  10. Your cell phone or laptop battery is a deep cycle battery. The same chemistry is becoming increasing used for RVs, cars, and other deep cycle needs. They are lighter and can be regularly discharged to 10% without harm.

    To get 400 ah of use daily you should have 800ah of led acid batteries but will only need 450ah of lion to provide the same 400ah.

    Once the manufacturing costs come down the old faithful lead acid battery is done for. Expect this to be happening rapidly over the next decade.

    1. There is probably going to be a market for somebody that knows how to make 12 volt lead acid batteries. How hard can it be? They’ve been around for a rather long time.

      1. Just looked it up. Wikipedia says lead acid battery invented by Glaston Plante in France in 1859.

    2. Been working on DC power supplies for 40 years.
      A good industrial lead acid properly maintained lead acid battery bank can last for 15 – 20 years.
      There are some issues with these types of batteries.
      (a) Must be ventilated
      (b) Must be handled properly with goggles, an acid proof apron and gloves.
      (c) Not overly environmentally friendly – but then again no cell or battery is.

      Lead Acid will not be going away. 80% of industrial batteries are still the Plante derived design.

      New fangled designs and fancy material constructions come up all the time. They all have some flaw which renders them a compromise.
      Battery technology is 150+ years old since Plante came up with a general design. If some miracle breakthrough in batteries was going to come out it would be here by now.

      Battery technology is limited by physics and the available elements. (materials)

      Cell technology has advanced in miniaturization but so has the technology relying on the stored energy from these cells or battery.
      Also remember that very small button cells have been around for more than 60 years.

      Many great battery announcements are made but these only work in a laboratory environment. Heat is the biggest enemy in battery design.

      F.W.I.W. European cars are featuring a stop/start feature now starting to be mandated by the European union. This feature has started to have unexpected consequences – e.g. Battery issues. The latest fad cadmium style high CCA relatively low AH capacity batteries are being found not up to the task of stop/start motoring. There is even talk of going back to lead acid.

    3. Li Ion batteries have a problem with heat when under heavy load, don’t they?

  11. When you buy a new battery there is often a deposit for the return of an older one. Usually $10.00 or so. I’ve found that they have a much higher return at metal scrap yards. $20.00 to $30.00 dollars a battery depending on the weight of the battery.
    We had 4 Trojan golf cart batteries on our sailboat. They did not hold up in storage over the summer and I can only guess at what the heat got to in a closed up boat in the Mexican summer. I know the temperature outside of the boat was up to 115 degrees at times. I’m presuming that the heat just evaporated the water out of the cells. Probably not much of a concern in many places but certainly something to consider for those of us in hotter climates.

  12. Hi all, Brain Dead here when it comes to Solar. I have actually been wanting to take the plunge for some time now, so I know it’s now research and reading time. Like most people I guess when coming into something new there are 5000 questions, so how about some “advice” for the research places, and maybe some pieces and part ideas (websites/books/links) without having to take out a loan on the house, dog, truck, car, AND personal insurance policy. And yes I’m a 100% DIY person.

    So with no BS, where is a great place to start? besides the check-book I mean.

    I did check on some of the equipment that No Joke has. might be a tad out of my reach. FYI, I think that guy is rich!!!! hehehehe.

    Thanks in advance

    1. Ken’s system is a fairly large system… copy it, tweak it. If you are in a dry sunny area it would handle an average home. Check your power bill monthly usage. Plan accordingly.

      1. Be careful, lots of solar energy systems shysters out there. Lots of junk. Costs are coming down, but just like with windows, a lot of contractors will only sell complete, installed systems. The installation more than doubles the cost.

  13. Excellent info Ken,
    Thank you much, have been trying to get info to set up a small system that could power basics in our home but its been like pulling teeth to get anyone to work with me, they all seem to only want to tell me what I want, not listen to what my goal is and give constructive advice, they also are primarily pushing grid tie and always only pushing permit apps and stuff.
    I could care less what sort of federal subsidies there are, i don’t want them.
    What I do want is helpful info, and this is a real good start. Was looking at gelled optima batteries for my refer truck farmers market setup, that is my #1 system I want to get together, the refer unit runs 65amps 12v when running, so want to put as many panels as possible on the roof and a custom built retractable awning with about 8 of the biggest optima yellow batts. they make, are supposedly good for this purpose, heavy as hell but supposedly will hold up to the combo of slow charge from panels and fast recharge off alternator and or generator and charger,
    Can get about 8 large panels on the truck between the roof and the awning, the goal is to be able to let the truck sit with refer running at farmers market without starting truck or generator to charge batts. or run refer.
    The other system that is also a priority is to run lighting and one refer in my house, that’s going to be s little more involved but still not too big, am going to look into the hardware more for that, but have been leaning toward just buying a kit from Iron Edison, they have one for about 20k that should work and then some and will have the nickel iron batteries, huge ass battery but way way better than a lead acid,
    Anyway, thank you again and looking forward to reading comments, got to go do some clearing, have trucks set up to haul road base tomorrow to clean up my parking area for my equipment.
    Aloha all

    1. Kulafarmer, I was surprised that nobody brought up the Edison battery before you did. Being a Nickle/Iron battery, I believe it doesn’t have most of the environmental drawbacks that the typical lead acid battery has. They are expensive, but also are very durable and can take much abuse from what I understand. I think it may be the way for me to go if I can finagle the finances!

  14. Many years ago when I worked in electronics we had a room full of “deep cycle” batteries. These were very large glass “jars”, five gallons or more with lead plates immersed in an acid. Very basic lead acid batteries. Their life cycle was measured in decades. They could be drawn down to 0% but typically they just sat there at full charge waiting a power outage. You can make these simple lead acid batteries After TSHTF.

  15. Can anyone put up a chart that specifies dod?
    It was stated that some 12 volt batteries are designed to withstand 50 to 80 percent discharge without damaging them, however obviously that doesn’t mean discharge them down to 6 volts.
    It might help to clarify what that means to someone just beginning to consider solar as an option.
    Not everyone knows that the inverters will shut you down before you destroy your batteries. But it might help beginners to understand a little better before they throw together a small system, then when the power goes out, they think they can power up 2 or 3 120 volt lights, a 42 TV, and a fan while watching a DVD then………..bam, no lights no nothing, and wondering what that noise is when the inverter alarm goes off. Also maybe explain what the battery amp hour numbers really mean. I have tried explaining to some newbees that just because you have a 100 amp hour battery, doesn’t mean that you can run a 10 amp power saw through an inverter, for 10 hours!

  16. You should write about iron-nickle batteries. They are said to last a 100 years or more. Will not be damaged by cold temps. And can be discharged extremely low with out damage.

  17. @everyone,
    When I was designing my battery system (48 volts) I did a cost comparison by getting company provided quotes for equal amp-hour systems. My flooded lead acid battery system cost $11,000 and the Iron-Edison quote was $71,300; equal sized battery banks. Which way do you think I went? Lead acid of course!

    Now let’s talk about the really expensive batteries, Lithium that is.

    Just for fun I went to a car junk yard and got several batteries out of wrecked electrically powered cars. I designed a control module for charging these batteries from my solar panels. Seems to work good. Now when my wife’s sister comes here I always charge up her electric car as we play bridge; a free fill up. She loves it. Notice I did not mention the brand of car! Guess why? It is not funny why!

    1. How long have you had your battery bank so far?
      I know what the suggested average lifespans are but do know some folks with trojan batteries that have lasted 10 years, so just curious about real world application, and real world numbers.
      The cost of the iron edison batteries is scary

  18. @kulafarmer,
    My batteries are only three years old. I chose these batteries because they are used by the railroads and after discussing this with the railroad maintenance crews they always get 10 years out of their batteries. I have known these rail guys many years and really trust them. Also, to get max. life out of a battery bank do not draw the battery down more than 30%, equalize the battery bank about every 3 to 4 months, and keep them watered( distilled only) and you will be satisfied. Best wishes.

  19. Heres a question,
    In order to draw 12 volts off of a bank wired for 48 volts i need to use a diode on the pos and neg leads that take the power off the individual battery? Or is it not possible or safe?

    1. @Kula, I simply wouldn’t recommend doing that, because if you pull energy from any ‘one’ (by itself) of the four batteries in a 48-volt string (rather than the whole string equally), you are upsetting the balance of the string chemistry/charge/re-charge, etc..

      Maybe ‘No joke’ will offer an opinion in this regard – given his electronics engineering background?

      1. Thank you Ken,,,
        Excellent input in these pieces, and lots of good info for a starting point from you, so thank you much!

  20. @Kula,

    I read your question and hesitate to give an answer. A diode is not needed at all. In a 48 volt system I will assume that you have 4 each 12 volt batteries in series. There is a right way and a very dangerous way to pull off 12 volts. The safest way is to only work with the battery that is closest to the bottom of your battery string; the battery that is first off your ground wire. Any other battery is really at either 24 or 36 or 48 volts with respect to ground and if hooked up to something that is 12 volt you will have a melt down of that device.

    1. I think ill just keep a separate bank and system for 12 V
      Thank you much for the input,

  21. Another question,
    Its ok to over size charge controllers or inverters or battery banks?

  22. @kula,
    1. Inverters can not be to big, you just would not be using all their watt capacity.
    2. Battery banks can be over sized, in the sense that the charge controller can not keep the battery bank charged up. It is not good to keep a battery under charged.
    3. A charge controller can to be too large in that if should be programmed so that it over not heat the battery bank during charging. Also, the controller should not charge the battery bank to a voltage that is too high. Both charge rate and the limit on charging voltage are always programmable. The battery manufacturer will provide this information.

  23. Larger inverters “may” have a larger drain on your system even when they are not loaded (powering anything from the AC outlet). In general alternative energy systems run best at around the 50% power level. Not a hard and fast rule of thumb but tends to crop up as the “ideal” in terms of efficiency and component life.

    Here is the “nugget” of good information about alternative energy systems that is often left out of the discussion: Use a heavy gauge wires on all of the 12V (or 24V) side of your system and keep the wire lengths short. Second make sure the connections and connectors are good. Crimp connectors “can” be adequate if crimped correctly but soldered connectors are better. The wiring on the 12 volt side of your system is the weak link and deserves extra attention if you want an efficient system.

  24. Hi all

    Something that I’ve not seen come upon any of the countless discussion forums that I’ve read, but a situation that my club faces…

    We are doing our homework in putting together a backcountry cabin proposal to BC Parks, and power / heat are components of the equation.

    We realize that a modest system consisting of ten, 300-watt panels and a dozen or so ‘glass-matt’ batteries, augmented by a pair of small wind turbines will do an admirable job of LCD lighting, small electronics etc., but we need power-enough to run a 500-watt room heater for long hours during winter nights as well…

    Have any of you ‘out there’ had any experience with this kind of continual current draw, using a wind/solar/battery setup?

    If so, we’re you able to pull it off successfully?

    The cabin is located at sub-alpine elevation, so wood / pellet stoves are out of the question, as are large bottles of propane…

    Appreciate your time.


  25. I’ve been installing battery based solar systems for 25 years and have replaced a lot of batteries. A long time ago I used to install golf cart batteries because they are the best choice of the choices you listed for many off grid systems but they hardly ever last seven years. Their big brother the L-16 is a much better choice for performance and longevity though in recent years I more commonly install industrial fork lift batteries with ten year warranties and fifteen year lifespans.I would use golf carts for some little hobby system or a small cabin and L-16 sized AGMs for folks that cant deal with watering batteries and dont mind their high price and short lifespan. Don’t even get me started about the Tesla battery, an overhyped product made up of Panasonic cells wired to 350 volts dc. The public hasn’t understood that last part fully. 350 volts will not do most of you any good and its designed for a grid tie system only.

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