Recently I bought new mobiles for myself and Nancy. These have huge batteries (5000mAh) which will last almost two days on a charge. Battery University has an excellent article on How to Prolong Lithium-based Batteries. One of the recommendations is to not full charge a lithium-ion battery, instead charging to 70-80%.
As luck would have it Ariela, the app I use for interconnecting our mobiles to Home Assistant, reports the current battery level back to Home Assistant as a sensor. Coupled with a TP-Link HS100 it became trivial to interrupt the charging of our phones at 85%.
- id: '1580492681958' alias: Switch:Adrian's Phone Charger:Turn Off description: '' trigger: - above: '85' entity_id: sensor.adrian_s_g7_power_battery_sensor platform: numeric_state condition: - condition: state entity_id: switch.adrian_s_phone_charger state: 'on' action: - entity_id: switch.adrian_s_phone_charger service: switch.turn_off
Some quick analysis of the sensor graphs shows that a charge to 85% takes around an hour. To maximise the phone charge during the day, I delay switching on the charger until the early morning (currently 04:00, but could be later).
- id: '1580492573046' alias: Switch:Adrian's Phone Charger:Turn On description: '' trigger: - at: 04:00:00 platform: time condition:  action: - entity_id: switch.adrian_s_phone_charger service: switch.turn_on
There is probably some further tweaking and optimisation to be done here. Time will tell whether it actually has an impact on the long-term life of the phones.