The reason why I ask this is because the damage from batteries which have been spent and are no longer usable damages the Earth much more than the strait gas engines do. Now the hydrogen fuel cells don't have that pollution, but those kind of batteries aren't what they use.
it takes more energy and pollution to produce the batteries for prius than to produce a hummer.
http://www.impactlab.com/modules.php?name=News&file=article&sid=11001