Ok this is going to be a funny story: So I installed iOS 9 with everyone else, and realized that it was draining my iPhone 6 battery quite a lot. I also use the watch so I thought maybe together with the watch, this drain was normal. But then I started seeing things like 60% battery lost overnight on standby, which didn't make any sense. So I restored my device and set up as new, as the last resort, 5 weeks ago. Didn't help. The same drain was there. So I thought, maybe it's a bug with iOS 9, so I made a bugreport and Apple told me to start logging my battery, which I've been doing for 3 weeks, and sending the logs to them. But last Friday, I had a minor foot injury and had to stay home for this whole week. Bored out of my frikking mind, I started playing with the phone and testing battery. I was restoring the device and not installing any apps and leaving the device on standby to see how much battery was draining. The battery was doing great without any apps. Then I installed apps and put in my music and made the phone usable again, and bam, battery started draining again. Then I thought about deleting my iTunes library and remaking it. I have around 60 GB's of music in my phone, so I thought maybe there's something wrong with the music files I'm putting in. I recreated the iTunes library, added all my music again, and restored the phone and set up as new device. Installed all the apps, synced music, and FINALLY battery back to normal with everything set up. So the problem I think was the iTunes library. Whenever I synced music to my phone, it would finish on the computer end, but it'd take some more time on the device for the sync icon to disappear. So I think the library file got corrupted at some point, and when syncing music to the phone, every time after setting up as new device or restoring from backup, some bad bits were being written to the phone. To be honest, I'm not surprised. Similar thing happened to me with my iPhone 4S many times. I'd sync music to the phone and the sync would just hang or stop in the middle, and only half the music would end up on the phone. Sometimes re-syncing would solve, sometimes it wouldn't so I had to restore from backup and try the sync one more time. And then I'd do the same trick, delete the library, remake it, and then the sync would go flawlessly. If you are dealing with huge iTunes libraries like mine (680 GB), things may get messed up every once in a while, which is a design flaw in the iTunes library structure for sure. Nevertheless, if your phone ends up draining more battery than usual, if you have lots of music in there, try this trick. And now off to reporting to Apple how I solved it. They should really fix that iTunes music sync.