At one point I was using an old phone as an IP camera and I had it plugged in to a battery bank that was constantly charging. The battery bank died pretty quick

At one point I was using an old phone as an IP camera and I had it plugged in to a battery bank that was constantly charging. The battery bank died pretty quickly, I think within weeks. Then I just plugged the phone directly into power, and the phone battery died eventually too (it started bulging, glad I noticed before it got worse). So yeah, Li-ion batteries don't like constant 100% power.