One of the most exciting things i've seen is the new nanotech battery development that has 10 times energy storage density as current batteries. It is a recent patent application and all major players in the use of batteries are very interested. I haven't seen any estimates on cost, but volume/weight issues for cars would seemingly put this development on the front burner. The use of current microtech manufacturing processes developed for manipulation of silicon can be directly applied.

"Nanowire battery can hold 10 times the charge of existing lithium-ion battery"

It's not a small improvement," Cui said. "It's a revolutionary development."

http://news-service.stanford.edu/news/2008/january9/nanowire-010908.html