It might be a bit overblown. People will definitely replace their cell-phone batteries by the time they get down to 50-60%. Car batteries would probably be not

It might be a bit overblown. People will definitely replace their cell-phone batteries by the time they get down to 50-60%. Car batteries would probably be not so great by the time you're down to 75%. Realistic real world mileage on a typical 220 mile battery, at 75% capacity, is probably more like 110 miles. The catch is that for grid storage, capacity along these lines doesn't matter to the same extent, as much as cost and retention. As long as we have cheap wind and solar, and they are able to manage fire risk, those batteries would just be sitting around.