AT&T. I just don't get it, I don't have a very high brightness, (set to auto), I'm using Package Disabler Pro, I have no Power Saving apps installed, I use WIFI all the time, the device on GSM Battery Monitor has 0% held awake, SOT is usually high, Most of the apps I use are restricted to background, Google Photos only sync with WIFI, I have location turned off, Google Now turned off, I deleted Facebook as I've heard that's a battery drainer. My accounts, well there's no option to sync Wifi or Cellular Network. Spotify only downloads my playlist over WIFI only. I Use Do Not Disturb at night, so nothing should come through except calls, and alarms. I've turned off vibrations on the phone as I know it drains battery. All bloatware is disabled. I have factory reset the phone, wiped the cache partition. My cell signal right now is at 4 bars, sometimes it decreases. It just varies, but I can't do anything about that from where I live. I do put the phone in airplane mode when that happens, but I leave WIFI on.
I think that's it.