Where do you think the energy comes from to charge the batteries every 2 or 3 days?
Think about the significant losses every time energy is converted from one form into another.
Oil into gasoline into car into miles
vs
oil into power plant fuel into electricity into car into miles
Which do you think burns the most oil in the end, and puts more pollutants intot eh atmosphere?
The marketing works well as the happy owner drives round with a warm feeling that he's doing his bit for the environment, yet he doesn't see the extra wasteage and inefficiencies further up the chain that in fact add more environmental problems than previously existed.