iMore

I've been using the 6s plus for a few weeks. Over time I noticed that the battery 'usage' and 'standby' times are always the same. Went to the Apple Store but the genius there didn't find anything wrong with the phone. Searched in forums but there doesn't seem to be any specific issue that is causing this. So this is my request: if you ever had the same issue and managed to fix it pls let us know how.
Is it a rogue app? Is it a corrupted backup? Is it anything else?
Thanks!