If you take the battery out of the scooter to charge, make sure the rubber stopper at the bottom of the battery is pushed back in, flush with the battery, before the battery is inserted into the scooter. If this rubber stopper is left out, it can get jammed between the battery and controller pin. If this happens, the battery cap will be more difficult to put in. This could also cause the scooter to not turn on at all.
If the battery is inserted while the rubber stopper is not flush with the bottom of the battery, it can also break off inside the scooter stem. This can then become jammed in the controller pin that connects with the battery and prevent the scooter from turning on. If the rubber piece at the bottom of your battery has a chunk missing (see picture below) please check inside the scooter stem for this possibility.