[Pxtl]

Lenovo's tablets are designed to be aware of this - after they've been plugged in for extra long (afaik 24H) they switch to battery-protector mode where they hover from 40%-60%. Hopefully somebody could steal this feature and add it to LineageOS or something. Edit: apparently you can do this on stock android with root[1]

[1]https://f-droid.org/en/packages/mattecarra.accapp/

[scns]

There is BatteryBot Pro on https://f-droid.org where can set an alarm for charging the phone you use till 80%.