Your iPhone rings an alarm when it’s over 80% charged.
You must do additional work. In the creation of personal automation, you can set the shortcuts to run when the low power mode is turned on.
It is recommended to use up to 20% and charge up to 80% to maintain battery performance.
This is a system that turns on the low power mode at 20% and turns off the low power mode at 80%. Therefore, the low power mode must be switched on when charging.