[05]

I don’t think you got that quite right. Most cellphone batteries are single cell (L shaped ones excluded). All cells have the property of degradation per cycle depending on range of charge/discharge (0-100 worse than 10-90 worse than 20-80). Standard cell phone BMS charges 0-100 because most manufacturers optimize for battery life per unit weight, not cycle count. Planned obsolescence and all that..

[eridius]

At the very least, the "battery" includes the circuitry protecting and mediating access to the cell(s), and that's the point where it would prevent the cell(s) from overcharging.