You have probably noticed if you turn your phone off and you leave your phone for a month without turning on the battery discharge a little bit.
Those are the reasons why this happens:
- your mobile phone is off but your mobile phone is still monitoring buttons to check when you will press turn On button and turn the mobile phone back.
- the battery has so-called self-discharge chemical reaction. The most used material for mobile phone batteries is Li-ion which has between 2%-3% self-discharge effect per month.
- when your phone is off there are some back processes which are still running example: an internal clock for time, alarm ring if your phone has a function to alarm in turn off mode etc..