Handling all those extra batteries would be complex and expensive. For one thing, batteries are not, and probably never will be, standardised between different

Handling all those extra batteries would be complex and expensive. For one thing, batteries are not, and probably never will be, standardised between different makes and models of vehicle. Most drivers, in most circumstances, would prefer to wait the extra 10 or 15 minutes to charge their own battery. After hours of driving, you probably want to stop for a snack or go pee anyway.