Apple's iphones fail to charge up to 80 percent of their charges, mostly because overheating limits charging. 16-22° is the best use temperature for Apple batteries, but our daily use is basically more than this value. Under normal circumstances, the rear cover has a certain perceived temperature for the battery has been overheated.
At this time, you can place the overheated mobile phone on the tile or glass, and it can be cooled quickly within 10 seconds, and then it can be recharged after cooling.
If you are sure that the phone is not hot, the temperature is normal, but still at 80% of the time will not charge, this generally happens on 11.4 systems. The solution to this situation is to use the phone power to automatically shut down before going to bed at night, and then charge the device. Do not use the phone during the whole process, wait until the phone is fully charged, and it will calibrate itself after full, and it can be used normally.