Self balancing electric scooters have Lithium batteries which recharge fairly quickly. The battery charger should not be left plugged into the scooter for more than 2-4 hours depending on how long the scooter was previously used for. If the battery charger is left on for more than 4 hours then it could possibly overheat and burn out. This has been the cause of many self balancing scooter battery charger failures that we have seen. Of course a well built high quality battery charger would not do this, however many of the original battery chargers that are included with new self balancing scooters are lower quality and should be unplugged from the scooter as soon as the battery has finished charging to prevent damage to the charger.