I’d like to use my old iPhone 7 to play music on a stereo system. The battery is essentially shot at 60% health, but the phone would just be kept stationary as a music player - it would be more convenient just to keep it plugged in.

My only concern is that leaving the phone plugged in could cause the battery to swell up. Is this likely to happen? Otherwise, I don’t care about the battery health degrading for my use case.