How can my electric car sell electricity back to the grid? How would the inboard computer know?,(reply>), Batteries have limited charge cycles, so I have to wonder what constantly draining and filling them would do.,(reply>), Presumably when it is charging and connected to the grid the software in your smart meter would be able 'ask' for some juice from your cars battery, the computer on your car likewise would be able to say 'yes I have plenty, take some'. Its all in the software, it'd probably be a setting somewhere that you can configure to say how much you want to give back, 10%, 20% for instance, so you don't wake up with a flat battery. Simple(ish)