I've never understood why companies force the battery to charge the whole time it's plugged in for things that charge quickly and discharge slowly. If a full c

I've never understood why companies force the battery to charge the whole time it's plugged in for things that charge quickly and discharge slowly. If a full charge lasts 2 months, then why keep it topped up while plugged in? Just charge it to 85%, then let it discharge to 50%, then charge it again. The circuit to do this can't be that hard to design.