In a post on the Apple Support Community, one user writes, “I have the same issue with my iPhone 11. I upgraded the other day and I have woken up every morning to find it fully drained. Yesterday I turned off WiFi, Bluetooth, all background app refresh, and ensured that Personal Hotspot was off. It was fully charged at 6 pm last night and not used. It ran out of battery at around 10 am this morning (so, around 16 hours later) with no use in the meantime.”
Now, some have suggested that this is “normal” and that usually after the initial update, battery drain can be normal as there are various background activities that are taking place that could cause the drain, but it should go back to normal levels in a day or two. However, given the number of user complaints, it doesn’t seem to be “normal” at all.
Apple hasn’t said anything about the battery drain issues yet so we’re not sure if they are aware of it or not. In the meantime, we suppose there’s really nothing that can be done unless you’re willing to downgrade to the previous version of iOS.