Actually, our very first prototype was a thing that sat on top your existing car battery. After talking to some people, it seemed like they preferred it integrated into the battery itself. It makes the price easier too, since you're not spending money on a battery AND a thing you put on top of it, just a better battery.

Industrial motors aren't something I've looked into a lot yet, but it could be interesting. I was just talking with someone the other day about using supercaps in robotics applications. Apparently some people are already putting small supercaps in the joints near the motors to help provide surge current during high accelerations or loads.