RE: New Batteries
I forgot to mention one modern solution, the Nuclear Battery.  More info
here:
http://en.wikipedia.org/wiki/Radioisotope_Thermoelectric_Generator
In use in many places around the globe and in space.  I had an acquaintance
working on these things back in the '60s.  He about had a conniption fit
when, after a vague comment by him about what he was working on I described
the operating principle and asked if that was a more precise description.
He said something to the effect of "We never talked about this." and ended
the conversation.  I deduced later he was working on these things to power
SOSUS, still a very dark secret at that time.
I don't know how small you can make one of these things but would be a hoot
to put one under the back seat......