Following one of the recent iodé updates (not sure if it was 5.3 or 5.4 as I did both within a few days) the new Battery Saver enforces its operation when the level gets down to 20%. I’ve always had it at 10 or 15% on both Android and my other old phones. If I go into the Settings → Battery → Battery Saver, and set a schedule to turn on at 15% that only holds until the phone is rebooted and then it returns to 20%.
As well as enforcing a half-broken dark theme that often renders some navigation elements illegible, and interrupting or crashing whatever I was in the middle of doing on one or two occasions just as the level drops to 20% (e.g. stopping a video recording), I’ll find I want to quickly use the torch for a brief moment but it’s been disabled, and I have to go into settings and turn battery saver off to use the torch.
I think I read in a thread here that there’s few configuration options so I might have to disable it altogether, if it will let me. The previous battery saver seemed more useful.