Chosen Solution
I ordered and installed a new battery for my 5s–it is certainly better than the old one, but not as good as new, and the phone still shuts off prematurely when battery life is below 20%. I wiped the phone and didn’t restore the backup, reinstalling data and apps, and it didn’t help. Is there some power management I need to reset?
Bad batteries are commonplace, so you could try that since they are inexpensive. Otherwise, I would worry about U2 damage from non-Apple charger usage. That is a board-level repair you’d need to send your phone out for.
