The problem is the charge controller. Mi bit starts drain battery after 3 years. In a day it drains about 20% of charge for no reason. I change the battery. It shows 100%. After two days the battery is dead and I cannot recharge it by the watch. With a voltage meter I measured the voltage on battery plug on the watch discovering the voltage by motherboard is about 0.3V an not 4.2V how it should be. Thus I think in a charge controller problem that drain the battery and not charge it.