IOS 9 Will Give Your iPhone up to 3 Extra Hours of Battery Life

Your iPhone battery will last longer with iOS 9.
At WWDC 2015, Apple senior vice president of software engineering Craig Federighi announced iOS 9 will extend battery life on iPhones by one hour. Another low power mode will extend battery life up to three more hours on top of that.
Federighi didn't specify what the extra three hours actually referred to.