I installed the ios 11 update on my iphone 7 last night. Updates sometimes slow older devices down. Click here for tips on speeding your phone back up. I haven't done much playing around with it yet, but I use my phone a lot & have to charge it often. Some people were given the opportunity to install ios 11a week early. Many complaints of shortened battery life have appeared in social media. Some of this is temporary, according to bgr.com. The process of re-indexing various features will use more of your battery than what you're accustomed to, and you'll certainly explore new features. The more you use your device, the more you drain the battery. If your battery still seems to be draining more quickly after the first couple days, go to settings >privacy>location services, and turn of the GPS function on devices that don't need to know your whereabouts. Virtually all of mine are turned off.