Advances in lithium chemistry might one day lead to batteries that provide 10 times the performance of existing batteries and cost one-tenth the price, said Winfried Wilcke, IBM Program Director at the Almaden Institute, a two-day conference on energy storage taking place at IBM's Almaden laboratory south of San Jose, Calif.

Improvements in performance by 100 times may not be doable, he added. Unless you are thinking about nuclear batteries.

What are nuclear batteries? They consist of a piece of plutonium wrapped in a thermoelectric material that can convert heat emanating from the plutonium into electricity. (Cypress Semiconductor and a new-spin out from UC Berkeley are two of a small number of companies moving into thermoelectrics.) Wilcke told me he's handled large pieces of plutonium. "It is a hot potato." Nuclear batteries can also be made with capacitors coated to harvest alpha emitters.

Long-range spacecraft rely on nuclear batteries. Past Saturn, it is a necessary source of power.

But for human, everyday use, they would be impractical and un-econonmical for all of the reasons you're thinking of right now.