New Power Power Wheels vehicles were designed with a built-in thermal fuse system to prevent the battery from overheating throughout use.
Older models have a removable 25-amp fuse to safeguard the battery from damages throughout use or when re-charging.
To find the fuse...
Unplug the battery from the Power Wheels vehicle, take it out of the car and lay it on the ground with the top of the battery facing up.
You should be able to see the fuse in the top of the battery.