A friend of mine recently bought a house and discovered a bank of deep-cycle batteries sitting in the shed left by the previous owner. He was only too happy to let me have them for a project, and all they cost me was the shirt I was wearing when I picked them up (the electrolyte spilled a bit).
The batteries are 2 volt, 200a/h units - most of them are still holding a charge of between 1 - 2.2 volts, although I suspect their capacity might be shagged. The only way to tell for sure is to try charging them with my trusty car battery charger, although for some reason I'm leery of hooking such a massive bank of batteries up to my tiny little charger. If I hooked six of them up in series, can anyone see a reason why it wouldn't work?