Solar Power for Dummies part 4: The Batteries

Garikai Dzoma Avatar

If you ask anyone with a Solar Power system what the most vulnerable part of their system is, you will no doubt be told it’s the batteries.

Batteries are perhaps the most delicate part of any off the grid solar system and while your solar panel is going to last for eons, it is unlikely going to be the case with your batteries. They are a constant source of headache and grief especially if you make mistakes during the buying and installing process.

Batteries perform the same function for electricity that a tank does for water. They store electrical energy in a chemical form that will be utilized during the periods when the panels are not charging. They also act as a reservoir of sorts to provide a stable source of power during the charging periods when there is a constant flux in the amount of charge coming from the panels

They also act as a reservoir of sorts to provide a stable source of power during the charging periods when there is a constant flux in the amount of charge coming from the panels as is likely to happen on a cloudy day.

Types of batteries

Before we delve into this sub-topic it is important to bear in mind a few things:

  1. The world of batteries is vast and constantly changing and this is not a journal article on the topic of batteries so we are going to breeze past the basics. Experts are free to chip in on the subject in the comment section.
  2.  It is unwise to use normal car batteries for your solar system, they are designed for quick discharge systems and are not suited for solar systems.
  3. Almost all types of batteries I know contain one dangerous chemical or another. You should not eat or drink when handling batteries and you should wash your hands with soap and water after handling them. Some batteries produce dangerous/flammable gasses and are not to be used indoors, in poorly ventilated areas or near naked flames.
  4. If you have watched action/spy movies you know batteries give a nasty shock. It probably won’t kill you but trust me you don’t want to be on the receiving end. To avoid risk of shock avoid handling both terminals at the same time.
  5. If you decide to be parsimonious when purchasing your batteries and end up buying a poor quality battery you will most likely end up regretting it. Always try to buy reputable brands of batteries. I am not going to recommend a single brand of batteries, there are too many. Just go the Gulf Complex or to suppliers of your choice and take note of the names of the batteries and go back home to research them first. Don’t just go with my guide!

There are many ways to classify batteries. I am going to ignore all these and tell you about the following types of batteries that you are likely going to encounter.

  • Liquid electrolyte (acid) batteries- these are the most common type of batteries. They usually require some form of maintenance such as battery water and acid topping or in some cases topping using a special concoction of the manufacturer’s choice. In the latter case make sure that this electrolyte is widely available. It wouldn’t do you much good to get stuck some months or years down the line if the supplier or manufacturer goes out of business and you have no way of getting the concoction. Make sure that the battery is a deep cycle battery. They are usually cheap costing around $1/AH
  • Maintenance free battery- these are also known as valve regulated lead acid batteries. These require significantly less attention compared to the normal lead acid batteries. They are usually sealed with non-removable caps. They still require cleaning though.
  • Gel batteries-a type of maintenance-free battery that uses a jelly-like electrolyte. They will cost you about $2-$2.50/AH at the Gulf Complex
  • Glass Mat batteries-sealed maintenance free batteries that do not produce emissions and are therefore ideal for home use. They will cost you about $2-$2.50/AH at the Gulf Complex.

The Ampere Hour

Just like with doctors and lawyers, the folks in the electricity business like to confuse us with their terminology. Battery capacity is usually measured in ampere-hours. If you remember an ampere measures the amount of electricity passing through a circuit.

1 Ampere-hour simply put means 1 amp for an hour. It means a 100 AH battery has a theoretical capacity to supply 1 amp for 100 hours ceteris paribus. Since we are assumed we will be building a 12 V system a 12 V  100AH battery produces 12 watts ( remember Power (P)=Current (I)XVoltage (V)) for 100 hours. In other words 1.2KWh! You can use the c

Since we are assumed we will be building a 12 V system a 12 V 100AH battery produces 12 watts ( remember Power (P)=Current (I)XVoltage (V)) for 100 hours. In other words 1.2KWh! You can use the calculator here to ease your calculations. Which would mean in Utopia one 100Ah battery would cover my needs which in part 2 we divined to be 1.24 KWh.

Alas! We do not live in Utopia, batteries in the real world hardly ever operate at a 100% and you should also never discharge your batteries completely. Not if you care for them or your pocket at all.

The general rule of thumb is to only discharge your batteries to about 50% that way they can last longer.  A discharge to 70% is even better. Then there are those cloudy days when your batteries won’t be fully charged. Taking into account the goulash of factors it would be a good idea (this is is not science) to triple your system requirements. Which means buying batteries with a 300Ah capacity.

Like with the panels, it is entirely up to you what type of battery or batteries you buy and the configurations you opt for. Three 100Ah batteries or as I did two 170Ah batteries.

Maintenance Free 100 Ah Lead Acid Battery$100
Maintenance Free 105 AH Battery$100
100 AH Gel Battery$200
170 AH Gel Battery$360
100 AH AGM Battery$200

We will touch battery configurations and wiring during the wiring installment, but it is important to note that you should only charge batteries using a regulator on your system or you risk damaging them. You should also constantly test your batteries and their performance to ensure that they are still working as intended.

The topic of batteries is long and winded and it is possible that I have omitted something important, or told a lie ( doubt that), if you have any questions, suggestions, tips please feel free to leave a comment.


  1. Joey.K

    I think I once asked this before , You wrote on imported batteries from “Gulf Complex” what about those made in ZIM (Proudly Zimbabwe). Can you please review the ones made in Zim, by battery type, size and price like you did here etc compared to Gulf ones. Thanks. Think Exide (Chloride) just launched a new Solar battery range. Are there any other manufacturers in Zim? how competitive are they?

    1. Garikai Dzoma

      Will do so shortly.

      1. $ajaxTransport()

        Will be waiting…

    2. Anonymous

      Battery World

    3. Maloon

      to be frank Joey,i am also a solar installer -i can do system design installation and maintanance.I have designed a wind turbine suitable for Zimbabwean market and i have had a fair share with local batteries. Zimbabwean made batteries are a disappointment.The hardly last 2 years no matter how much you try and take good care of you.Even the manufacturer doesnt seem to have her product knowledge.About 2 months ago i had a potential contract with a local company for solar installations and they were advocating that we use Zimbabwean products where possible.I went to a local battery manufacter as i was asking questions pertaining the batteries -particulary the technical specs – i was moved from office to office and guess what the whole company didnt have a datasheet for the products they are manufacturing bet yet explain the technicalities.So as a customer how can i have confidence in their products when they the manufacturers are not even sure of what they are manufacturing.

  2. Itai SolarSky

    Hi Garikai. Great and well researched article there.

    Consumers would do well to be wary of vendors in the flea markets. There is a consortium of traders supplying cheaper batteries albeit void of warranty.

    Most of these batteries are bought from auctions after 2-5 years of use in projects done by local NGOs. It is highly likely that you will purchase a battery that has been working at a hospital in a remote area and is nearing the end of its lifespan.

    Some well known motor spares shops are selling simple lead batteries passing them as Dual Purpose with the words deep cycle somewhere in there. When buying solar the best choice is a VRLA and GEL and insist on a new battery and warranty.

  3. Master_Shifu

    Hi Garikai,
    I am a little bit disappointed you missed out a few important points (in all your articles). Well, maybe I shouldn’t be.
    It is important to note that with enough care a battery can last a long time – typically 10years. Yes that is not the “rated” time and out of general ignorance people here have the notion that 2 years is good for a battery.
    I am distressed to have to say it but unfortunately many of the “professionals” here don’t know what they are doing. (Generalizing – there are some great, knowledgeable experts around). I have seen a number of “professionally” installed 2.5kVA – 3.5kVA systems installed with only 4x 12V 102Ah batteries – (that is batteries “enough” for 4.8kW (100A) for 1 hour). No.No.No.
    This is the vital information. Expensive initially, yes, but long term this is what one needs to note. Lead Acid (or SilverCadmium – or whatever deepcycle you use) loose their capacity and/or ability to supply power when drained too flat (like you said), charged too high or get too hot. Every battery has an internal resistance and according to your formulas you can deduce that the more current you draw from a battery the more power it wastes and the quicker it heats up : P = I^2 x R (Power = Current squared times Resistance).
    To cut a long story short. A rule of thumb is that you should draw a maximum current of 1/14 (some use 1/10) of the rated AH of the battery (and charge at the same rate or 1/10). So your system should not load the 102Ah battery higher than 10A – that is 120W (per 102AH battery).
    Therefore a 2.5kW system needs 20x 12V 102Ah SLAs – and herein lies the 150year old catch. I am using my 102Ah battery at 1/6 of rated capacity (+/- 200W) so you could get away 10 batteries for 2.5kW system, – 4 batteries – NO.
    I have a 102AH 12V deep cycle SLA I have been cautiously abusing in my office and it is now 4 years old and still happy. AND I expect to get at least 3 more years out of it (under abuse).

    I guess most of your readers will not come back to this but anyway there you have it.

    1. Tina

      Master_shifu please may you help me make a better informed decision I need to install a CUPS system at my parents home, currently they have a 4kva generator so I’m looking in the range of a 3.5kva inveter system to work during power outage times. what battery capacity is most ideal without for that?

      1. Master_Shifu

        Hi Tina. By cups I assume you mean continuous uninterruptible PS. My suggestions depends very much on what you want to power. Fully charged SLA batteries can handle high current for very short periods (eg. 60A for 2 min). I’d stick to cooking and boiling the kettle on Gas. Wire all your power saver light bulbs to the inverter and the TV and DSTV decoder (or laptop power point). It is a little more work but I would not wire the whole house to the inverter (if you want value for money). I invented an extremely power efficient (92%) LED system which runs of a 20Ah battery for a week. (Why did i say that? – oh. you don’t need much power to have good light).
        Best advice I can give is to look at the battery you want to buy, the good ones have a label stating how much continuous power they can supply with the maximum loads etc.
        Off the bat for your 3.5kva inverter 24 x 102AH 12V batteries is too expensive. 10x 102AH will do, 8 is pushing it. Best value for money – use gas and generator for cooking and fridges and charging batteries, then wire small inverter 1.2kVA and 4x 102AH batteries to TV and “saver” lights (don’t use incandescents!).
        Correct approach is to calculate your total power needs (TV/laptop + Lights) and put in a system 2.5 time bigger (eg. TV + lights = 300W – put in a 750W system, with 6x 102AH batteries (3 minimum – if you can’t afford 6)
        Piece of experience without the maths: TEST your system! if full batteries last on your full load for a minimum of 4 hours you should be OK(-ish).
        If you need more info. you can send an email request through

  4. mkaputi

    need to power an egg in incubator rated at 500watts for 12 hours a day, how many batteries do I need?

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  6. clement

    i have a small issue that i require help
    what is the effect of using a 200ah and 170ah in the same system or just using different batteries with different AH

    1. Garikai

      There should be no problems at all.

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