Phone batteries have relatively little margin. If it lasts barely a full day at full capacity, going down to 80% means you can no longer reliably say "I'll cha

Phone batteries have relatively little margin. If it lasts barely a full day at full capacity, going down to 80% means you can no longer reliably say "I'll charge it overnight". A car battery that lasted 300km new but now only 200km is still entirely adequate for a commuter with a 25km typical commute, and occasional 75km days out.