Install sys-lite. Then wait until your battery is under 20%.
Start sys-lite and go to the charging screen. Charge your iPhone to 100%. Do not stop charging. Let it 'trickle' charge the battery. You will hear a sound, when it finished with 'trickle'
Repeat this procedure once a month.
- Battery app. For example sys-lite. It is free.
Netherlands. Nearby Amsterdam.