estabya
macrumors 6502a
That is a classic issue related to the battery itself.
My phone didn't do this from iOS 7.0-9.0.2. Started on 9.1 for me.
That "something" will most likely not be iOS 9 (unless it is a relog of an online account of some kind). Check your usage and see.
I am familiar with iOS and battery usage. It was not showing any app that was being used in the background for nearly that long, and background app refresh was turned off. Again, this first occurred for me with 9.1.
Day one after a restore in iTunes and iTunes backup restore seems to be looking better. Time will tell.