My friend and I are trying to get some life in our "terrain vehicle" (http://offroad.no/?Page=Rig&Mode=View&RID=74), but the fourth battery we've found also seems to be put to rest. And today I started wondering; how does a perfectly good battery turn into a battery that doesn't work? As far as I know, you can just recharge a flat battery, move some electrons from one place to the other, and it should work again. But it doesn't. Why?

There are chemical reactions that go on the side that slowely use up the chemicals and change them to other forms that cannot produce electricity.

Batteries wear out.

If you're talking about big lead-acid batteries you find in cars, cells can short, and sulfur (from the acid) can build up on the lead plates over time so the chemical reaction slows or is halted completely.