just upgraded my 6S Plus to iOS 11.2.1 and got the worst ever battery performance: within 30 minutes, from 70% down to 10%, does anyone has the same problem? Can I downgrade?
iPhone 6 Plus, iOS 11.2.1
Battery usage may stabilize once the phone has been used on the new iOS for a while.
If not, and this is the original battery, you might make an appointment at the Genius Bar or at an authorized service provider to have the battery and phone evaluated.
Sounds like your device is "indexing" the content, which is normal with a new iOS. It is a very energy intensive process. It can take more than 12 hours to complete, depending on what you have on your device. Give it a couple days to see what happens.
You have a limited time to downgrade and you need a backup of the old iOS. You can't use a backup made with 11.2.1 to restore to 11.2
Worst ever battery performance of iOS 11.2.1 on 6S+
