Actually I've never thought
Actually I've never thought about this issue before but it makes sense. I HAVE used rechargeable batteries before and they ALWAYS get hot when I'm done; I don't think I'm even overcharging them, just charging normally but they get really hot when done. I can't even imagine charging a battery that can power a car. Sure they are spending a ton of money for the research but it's necessary to ensure the safety of drivers.