The battery life in iOS 10 up is not good. It drains so fast so better stick with iOS 9 coz if you start upgrading your phone to iOS 10, you can never downgrade your phone anymore. Apple never signed iOS 9 updates unless your phone is jailbreak.I’ve updated mine. Battery seems to be on par compare to IOS 9. The main reason to upgrade for me is the display accommodation feature introduced in IOS 10, the ’color filter’ turns my yellowish screen to a more bluish screen similar to other iPhone series. If you are annoyed by se yellowish screen, as update is highly recommended!