https://qz.com/1100556/iphone-battery-draining-quickly-on-ios-11-try-this-aapl/

If you’ve noticed that your iPhone’s battery seems to be draining considerably faster since upgrading to iOS 11, you’re not alone. And this might sound like something you’d read on an internet banner ad you wouldn’t click on, but hear me out: This one weird trick might fix our battery woes.

With the new operating system, it seems that Apple decided to automatically turn on “Background App Refresh,” a function that allows apps to constantly update and pull information from the internet even when you’re not actively using them. While you might want this for certain apps, you really don’t need it on for every app. I was seeing the battery on my iPhone 7 Plus drain in a matter of hours, when previously light usage would see it lasting the entire day.