I restore my 15PM to factory setting and here is my test with all other apps closed and all other apps background refresh turned off, all third party apps uninstalled:
Found this video on youtube:
- With IG open, Just opening the app and look at my profile for 1 hour, without scrolling or any interaction, battery drain is 20% per hour.
- With IG on the background app refresh enabled: 10% per hour.
- Without IG (app uninstalled): 3% drain per hour at idle
I just deleted Instagram off my phone. We shall see if it’s the culprit.
Based on this thread it seems likely.