Since most would plug in at night, or "Off Peak", it would help operators balance out the grid. Also in some states, you'd get a break on price by charging up off peak.
Don't "hybrids" charge themselves as you drive? Do you need to plug these battery systems in, or does the car charge it as it is being used? In hybrids, the electrical system are not always on, so don't they recharge when they're not being used? -Trey