Sudden Battery drain, not iOS 9.2, solved
A few days ago my battery suddenly started draining fast. Classic symptom: In Settings/Battery Standby Time was equal to Usage. (see: http://appinstructor.com/blog/2014/the-ultimate-guide-to-solving-ios-battery-dra in). It was not caused by 9.2, because it was almost a week after installing 9.2. Here is the troubleshooting procedure I followed:
- Reset by holding HOME and SLEEP until an Apple logo appeared - not solved
- Killed all apps after double-pressing the HOME button, then reset as above - not solved
- Turned off Push email - not solved
- Checked Settings/Battery; the top app was Calendar, at 78% of battery usage - this narrowed the search
- Knowing that sometimes an MS Exchange account can cause heavy battery drain, I deleted my Exchange account and reset - not solved
- Additional clue: In OS X Activity Monitor on my Mac the Calendar app was using huge amounts of data transfers - over 1 GB
- The only other source of Calendar events was iCloud, so I turned off iCloud Calendar and reset again - Battery drain stopped
- Added my Exchange account back - No additional battery drain
- So the problem was related to iCloud contacts. On a hunch I left iCloud Calendar off overnight. When I turned it on again the battery drain did not return - problem solved.
- The heavy data usage in Mac OS X stopped when I turned off iCloud Calendar.
While I can't explain why this worked, I can speculate that there was data corruption in the calendar database, that somehow was fixed by leaving it off for a period of time.
iPhone 6, iOS 9.2, 128 GB