If it means anything. My phone started to eat battery. My phone (14 Pro Max) was draining with nothing running and the absolute minimal usage. I tested it and made sure everything was turned off, Siri, background app refresh, brightness, you name it, it was off.
The genius bar ran tests last Wednesday, stated something is wrong with it and haven't gotten it back yet. Prior to that I was getting around 4 days per full charge. I updated to 16.1.2 and with no obvious change. Its extremely frustrating as Apple provides no real updates on what is going on nor when I will have it back. I expected more from them.
"Steps to Reproduce: Ran Mobile diagnostics
Ran battery usage diagnostics
Viewed battery life in diagnostics, there is a sharp noticeable decline in battery life even when device is not actively in use
Viewed settings such as Always on display, background app refresh and toggled all off
Customer states they already restored device using iTunes and set up as new at home"