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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:
  • 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
Found this video on youtube:

I just deleted Instagram off my phone. We shall see if it’s the culprit.

Based on this thread it seems likely.
 
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