All devices successfully updated to 11.3. My iPhone 7Plus ( June 2017) battery 100%, my wife's 6plus ( Aug 2015) battery 97%......both iPads (her iPad Air2 & my Mini4) no issues. Our battery discipline has ALWAYS been charge whenever power available ie usually when at home, including at night, all devices. Try not to let charge drop below 40 %', and let the internal wizardry sort out the rest. We've followed that protocol since iPhone 4S days and never had a phone die due battery......