Since upgrading to iOS 9.2.1, I'm having major battery issues with my iPhone 6s. When the iPhone is not being used and locked, battery percentage keeps dropping by approximately 15-25 percent every single hour. During that time, the iPhone is absolutely not being used and there are no incoming notifications or whatsoever. All applications are closed in multi-tasking, and background app refresh is disabled. When going to Battery in Settings, the Usage Time keeps increasing when the iPhone is locked. There is however no clear application listed which might be the issue. I even upgraded to iOS 9.3 beta 4 this week, but that didn't solve the problem. I've tried a several approaches to solve this problem: - Turning off and on - Hard Reset - Clearing RAM - Restore all network settings - Disable iCloud Photo Library, iCloud Keychain, iCloud Safari - Remove all Mail accounts - Restore to iOS 9.2.1 with iCloud backup by iTunes - Upgrading to iOS 9.3 beta 4 - Fresh clean install of iOS 9.3 beta 4 with iTunes, no backup restore The only way I was able to "solve" this issue was to disable iCloud, so it might be an issue with iCloud syncing. When I connected my iPhone with my Mac to Instruments (part of Xcode), I was able to view running processes on my iPhone. One of the processes that was almost constantly using CPU is syncdefaultsd (5-10 percent most of the time), even when the iPhone is locked. Via Google I found that this process is part of iCloud syncing, which might confirm my guess of iCloud being the issue. It seems like this process is preventing my iPhone to go into "sleep mode". I also took a look at the processes running on my MacBook Pro, and I noticed that the exact same process is eating up to 10-40 percent CPU every 5-10 seconds for 2-5 seconds. Is this normal? Maybe I have some issues with my iCloud account. Any suggestions what I can do to solve this weird battery problem? Does someone have the same issues? Turning off iCloud is no option for me.