Gasoline is a better store of energy than batteries, pound for pound.
Furthermore, federal crash standards and auto accident lawsuits prevent the implementation of light-weight cars. Burt Rutan, of SpaceShipOne civilian space flight fame, made a 4 passenger car for GM that weighed only 600 pounds, for instance. It was driven in a Wesley Snipes movie, as they had no other use for it (couldn't sell it commercially).
Lithium batteries *could* power a 600 pound car (think: electric golf cart).
But you need more energy for heavier vehicles, obviously.