The problem is that the battery is not the only expense on the car. You have to depreciate the vehicle's value too, because there is a good chance a BEV will be

The problem is that the battery is not the only expense on the car. You have to depreciate the vehicle's value too, because there is a good chance a BEV will be disposed of rather than have a battery replacement. Say the lifespan of a battery is 10 years. If you lose 10% of the charges for grid storage you're looking at replacement at the 9 year mark. Until we know that the vehicle itself will be reusable at that point you need to depreciate the battery usage against the cost of the entire vehicle, and be compensated for it.