charging – Making a device to simulate low battery early

I have device which is used commonly by a layman kin. She does not really understand, why spares the battery if we do not wait until it goes to zero. She thinks, the device needs charge only if it was powered off due to battery exhaustion. I have no way to change her mind, but I can install or set up on her (non-rooted) Android as I want to (including adb access, if needed).

I think, maybe some app could power off her phone if battery level goes under, for example, 35% or so. Alternatively, maybe the battery load calibration could be changed to consider the actual battery level lower as it really is.

What to do?