The only problem with this of course is that the range of a car is already limited. Plugging in your car overnight, and then discovering half the charge is gone might be a tad, shall we say, unwelcome.

One could imagine though a big incentive (cost wise) not to charge the car during the day, or early evening but have the charger kick in after say 10pm. Then if your range is sufficient to get to work and back you're not motivated to charge during the day.

While all those batteries sitting there is somewhat appealing, the highest demand for grid power is also likely to be around the time you want to use your car.