Well, that's a dumb thing to look at. I'd start with the amount of earth that has to be moved to make the batteries. I'm not saying I know, but it seems like a dirty and energy intensive process to mine all those materials. All US cars are ridiculously overweight these days (due to safety and emissions regulations -- the motors keep getting smaller). It masks the weight of the batteries. Try comparing a Lotus Elise with a Tesla Roadster.