One that recharges itself continuously via radioactive decay? I wonder if, regulatory challenges aside, a radioactive decay trickle charge could be enough of a trickle charge to meaningfully extend daily battery life...
Basically instead of having a big complicated nuclear reactor, you just throw some radioactive material in a package, let it decay, and generate electricity off the heat. It's mechanically much more simple and has the bonus of not involving critical masses of radioactive material ;)
Not very realistic though. Besides the obvious issues of carrying around lumps of plutonium, they're rather bulky, and disposal is a pretty major problem.
