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Why are there so many different types of battery?

(Click to enlarge photo)

This is rather a large question and is a bit like asking why are there so many different types of musical instruments! The simple answer is that each type of battery is best suited to a different situation. They are, of course, all doing exactly the same job, and that is to store electricity. For the purposes of an energy project, it all boils down to storing the most electricity for the lowest price taking account of how long the battery will last being used in a particular way. This is always going to be a judgement issue and one person's choice might be very different to another's. (These are not my batteries in the photo by the way, I can only dream of having such a large quantity!)

Our old friend conspiracy rears its head again here because there are those who claim that recent developments making batteries much more efficient and cheaper have been held back to maintain high use of conventional fuels. I am not going to enter this debate now because I doesn't get us anywhere, all that concerns me is what batteries are available now.

The rules to make batteries last a long time are very straightforward. Don't allow them to charge so fast that they overheat, don't discharge them any more than absolutely necessary and be highly vigilant about maintenance. The average car battery might be expected to last around five years but some fail before that. Some might go on for as long as twenty years - why. Usually this is due to two things: The quality of the battery in the first place and what has happened to it during its life.

Because price is such a big issue for energy systems mostly we use lead/acid batteries because they apear to be the cheapest but, be careful, some more expensive batteries might last longer which alters the calculation. Second-hand batteries can be very tempting but be careful making that decision as they are extremely difficult to properly evaluate and you won't know what has happened to them previously.

If you can afford it and have the space, buy a much bigger battery than you need and try and design your system so it is constantly trickle-charged. If you are using the battery with a wind system where there will be long periods with no charge, make sure you build-in an alternative charging method so the batteries don't discharge too far. This doesn't necessarily mean using the mains or a petrol generator as an engine can run on methane or wood-gas. Some people have found ingenious solutions for this and its well worth looking at other ideas on the Internet. Solar-panels are an obvious complement to a windmill but beware those dark, still winter days, you are still going to need something else on occasion.

My advice is to keep it as simple as possible at the start and build up your battery knowledge until you are ready to invest in a battery large enough to do everything you want.