My iPhone 6 battery was doing well...about 9 hours of usage and half a day standby put together. I had this kind of battery life on iOS 9.1 and recently with 9.2; I decided to reset all settings just to make sure there weren't any bugs, but after I did that, my battery life went downhill. It drains every couple of minutes with use and a few percentages on standby every couple of hours. I put all my settings back to what I had them before I reset the settings, so I have no idea what's going on.