This is the bane of my existence right now. I think I updated my iPhone 7 on Tuesday to iOS 13.1.2. I didn't notice a problem on Wednesday because I was only at work a few hours. Yesterday was my day off.
I got up to go to work this morning and took my phone off the cradle (Apple Lightning Dock) and drove to work. I pulled my phone out of my bag and the battery said it was at 1%. I thought maybe I had disconnected it from the wall so I plugged it in at work to charge. By 2pm it was at 100% so I unplugged it and put it back in my bag. By 4pm it was at 63% and by 7pm it was at 39% so I shut it off. Fast forward to 11pm when I turn it back on and it says 38%. I plug it in and get it to 65%, and by the time I get home it is at 9%.
Anyhoo, I tried to use a backup from August to restore it back to iOS 12. It restored to the backup but then it started updating back to 13 all on its own! Now I spent an hour rolling back a phone just to end up back at square one. However, the battery now says 85%!! And it wants me to re-update my watch and iTunes?
I have never had a problem before, and my battery health according to my settings is 90% original function.
I can tell you right now that I am not upgrading my laptop to Catalina anytime soon. ABSOLUTELY NOT!!
Now, I can tell you most frustrating part is, that during this whole scuffle my watch somehow got unpaired from my phone and I have to reset that too. GAH!!!!!!!