SUMMARY Batteries live longest if kept between 20% to 80%. It would be nice if KDE Connect could notify the user on the desktop side of things if a specified battery charge has been reached.
I'm currently using MacroDroid to just show a notification on Android when the battery is full. It used to then wait 1 second and immediately clear that notification again, because it would still arrive on my laptop, but now KDE Connect clears notifications from my laptop when they are cleared from my phone (which is normally good, but xkcd.com/1172 breaks my workflow), so now it instead gets cleared when I unplug my phone. The only time this setup could get annoying would be if I actually used my phone while it's plugged in and fully charged, which I pretty much never do, but that doesn't apply to your usecase. And it's obviously more setup effort.