Photos: Speedy sports car powered by batteries

The X1's license plate, which makes the car street-legal in California, indicates how it compares in energy consumption with a regular car. The car uses about 200 watt-hours to go a city mile. A gallon of gas contains an energy content equivalent to 33,705 watt-hours. Divide 33,705 by 200 and you get 168.5 miles per gallon. But 170 reads better on a license plate.

Photo by Michael Kanellos/CNET News.com