Electric cars' batteries are the most expensive component of the car. And they have a limited life, meaning that anytime the battery is charged and discharged, it loses capacity and at a certain time it will have so little left that it will have to be replaced with a new one. Therefore I would not let others use my car's battery for free, and also I would not like to find it discharged when I need it charged because "the national grid demanded energy". <br>This are the reasons I don't think electric cars batteries will play a significant role in stabilizing the grid.