I have downloaded iOS 11 before the native release on my iPhone 7 Plus. and I also having trouble of after installing iOS 11 Battery issue my iPhone. But i tried given steps and easily get rid of on issue.
– Disable notifications
– Enable power saving mode
– iPhone charging comfort zone, Use Original USB cable
– Disable location services
And more solution with screen here : https://www.howtoisolve.com/improve-ios-11-battery-life-iphone-ipad/
