1, the decline of battery health is due to the decline of the maximum capacity of the battery after a certain number of times of charging and discharging, which is irreversible, that is, the decline of the maximum capacity of the battery cannot be reactivated to the maximum capacity by simply charging and discharging or not replacing the battery;
2. According to Apple official website's introduction above, 100% discharge is not needed, and Apple lithium-ion battery works in charging cycle mode. If the used (discharged) power reaches 100% of the battery capacity, you have completed a charging cycle, but it is not necessarily completed in one charge, so you only need to charge it in time when there is no power, and don't wait until it is lower than 20%. However, after each charging cycle is completed, the maximum capacity of the battery will decrease slightly. After several charging cycles, at least 80% of the original battery capacity can be maintained. If it is further reduced, the battery needs to be replaced in time.