They won't have zero value after 10 years. But depending on how much the battery wears out, and how much tech and costs advance during that time it could make sense to put in a replacement battery with better than OEM performance. This happens to an extent now with hybrid vehicles, you can get an upgraded battery pack for about $2k all in. An OEM battery is $2500 plus labor. Tesla retail price for a replacement battery is $16k right now, aftermarket for EV would be less. Even factoring in the full OEM price for maintenance, once you account for all of the other maintenance and fuel cost an EV is price competitive overall.