Really good batteries (NiMH) are possible for electric cars, but there is a little problem: Chevron owns a controlling interest in Cobasys, the company that holds the patents on NiMH batteries. You can read about this here:
http://en.wikipedia.org/wiki/Nickel_metal_hydride_battery

Look at the section on Patent Encumbrance. Cobasys "is not interested" in small production runs, so it is impossible for small companies (much less enthusiasts) to get large format NiMH batteries. They are starting to make batteries for GM. But of course, some think their parent company bought the controlling interest to slow any switchover away from petroleum fuels.

This makes John McCain's big prize for a super battery rather silly: A good enough battery already exists! But almost all of the home-built electric cars use old-style lead acid batteries because the biggest NiMH battery you can buy retail is an AA cell. Thanks Chevron!

I think the Tesla uses lithium ion batteries that cost much more, hold more power, and are much trickier to manage in terms of charge and discharge without exploding!