I regretted upgrading from ios 9.3.3 to 10.2.1. I agree performance is smoother, but lot of battery drain. overnight there used to be only 1% drain in earlier version, but now it is like 10-11% throughout the day I used to charge once A day in earlier version, but now im charging twice.
I had the best battery life in ios 9 better this be a lesson, so people who are still on ios9, remain there do not upgrade unless you really need the new features in the newer ios. stay happy with ios9 if you want a decent battery life.