Very pleased to report that at 'update +48 hours' battery life appears to have stabilized at pretty much what it was on 11.4 ( which was good). I didn't do any 'knee-jerk fiddling' when in the early hours it seemed a bit down, but figured it was an indexing & settling out through the iOS & App spectrum. I have ( since 4S) always plugged in any and all devices overnight, -FORGET the old beliefs from pre li-ion days- and wherever / whenever a cord is handy. Other than my iPhone 6, which had chronic battery problems then a swollen battery ( demise of the device for me
) I have never had battery life problems in iOS....
This comment reflects my updates to Pad Mini4, iPad Air2, iPhones 6Plus,7Plus,8Plus