After being used for a period of time, the battery will "age". The specific manifestations are: the internal resistance increases, and the voltage at both ends rises relatively fast during charging. As a result, it is easily judged by the charging control circuit as already fully charged, and the capacity naturally "drops". Due to the higher internal resistance of the battery, the voltage drops significantly and quickly during discharging, and the system easily misjudges it as insufficient voltage and power (in fact, there is electricity but it cannot be discharged). From the above description, we can see that the aging of the battery is a vicious cycle. When you find that the battery's working time decreases rapidly, you should "exercise" it, otherwise it will eventually be scrapped.