On some machines, after charging for more than a certain period of time, if you do not remove the charger, then the system will not stop charging, but will also start the discharge-charge cycle. Perhaps the manufacturer of this approach has its own purpose, but it is obviously not good for the life of the battery. At the same time, long charging takes a long time and often needs to be carried out at night. In the case of China's power grid, the voltage at night is high in many places and fluctuates greatly. As mentioned above, the lithium battery is very delicate, it is much less resistant to fluctuations in charge and discharge than nickel, and this brings additional danger.