I have the iPhone 6S and it was superb on iOS 9. I decided to update it one day to iOS 10.whateveritwas and the battery overnight became horrendous. The phone didn't run slow but the battery would be awful. I would start work at 7:30am on 100%, literally have all apps closed down and no settings changed, i would come to my break at 10:45am and the phone would be on 6%-12% battery. I then updated to 10.3.1 and the battery still wasn't great. Got the battery replaced with Apple and it was ok after that. I've had previous experience with earlier iPhones of updating to the 'next' iOS and it making the phone run slow or the battery life be horrendous (or both) which puts me off updating to iOS 11. So both my wife and I have the same iPhone 6S phones - i got mine on release date but got the battery replaced a year later whereas she bought hers a year later and hasn't had a battery replacement. I'm currently experiencing no battery issues whereas she's experiencing quick drain at times. We're both on iOS 10.3.1. I'm curious about iOS 11 whereas she'd like to update to it. Is it worth it? Especially with the situation i've listed above? What about the battery life after the update and the phones responsiveness? To be honest the battery life concerns me more than the responsiveness of the phone after the update.