I have an iPhone 6S, and it recently started behaving strangely. Woke up last week to find it was down to 10% battery after having been fully charged before I went to bed. I shrugged and charged it up again. It went to 100% in just a few minutes, which was strange. From that point on it wouldn’t hold a charge, and would drop precipitously in moments.
So I figure the battery is going bad. No big deal, I’ll go to one of those mall fix-it stores and have it swapped out. Was on the road working, so it would have to wait a few days.
But now I notice strange things are happening. I get little cloud icons appearing next to some apps. They start re-downloading themselves. Those goddam songs by U2 that Apple forced on us a while back re-appear in my music library (I deleted the hell out them long ago). I have updates turned off - it’s not supposed to change IOS versions without me doing it manually. So I have no idea why the phone is doing this stuff, but I have to assume it is related to the battery issues.