Li-ion battery natural discharge
All batteries are discharged due to self-leakage current when stored for a long time.
However, among many batteries, lithium batteries have the least self-leakage current.
As you can see at the bottom of the table above, 5% drops in one day after full charge, and 1~2% in one month after that.
If the safety circuit enters, it is discharged by +3% more. Therefore, a battery with built-in protection circuit is not necessarily good.
And when storing for a long time, it is better to charge it to about 50% (3.8V) and store it than to store it in a buffered state (4.2V).