>>509469263anything explosive in an overhead locker is a risk not worth taking. you can't see what's happening inside the locker, so your response is delayed. the locker is usually full of flammable clothing and fabrics, the cabin is a confined environment full of nervous and easily panicked people. if you happen to have morons seated next to a burning locker, there is every chance that they will block the aisle in a frenzy and slow down the cabin crew with the fire extinguisher enough that the blaze gets out of control.
i assume this ban is only for overhead locker storage and that batteries are allowed where you can see them and respond quickly, i.e. on your lap or beneath your own seat. this is normal for most airlines in the world.