Battery at 91% ,,, play ringtone

Lithium ion battery chemistry demonstrates extendes life if not stressed to a full 4.2v/cell charge. I have no issues getting through a day on a partial charge (about 91% in this rule) and use this rule to minimize battery oxidation which accelerated at a maximum charge. The trigger level can easily be adjusted to play an alarm sound of choice. Read more about Li-ion battery chemistry at batteryuniversity.com and elsewhere.

Battery above 93%, alarm/sound

Since it is generally healthier for lithium batteries to be charged to slightly less than a full 4.2v I have a ringer/sound play so I can stop charging at a known charge point.