According to this
New York Times article, a startup named A123 Systems has created a battery that has very high power density (ie, you can store more voom in a smaller space).
The idea is that these would be used in hybrid vehicles, with potential performance of 120 mpg ... I'll leave it as an exercise for the reader to convert that into L/km.
I don't drive, so I have no idea how good that is compared to the average car, but it sounds impressive!
