It won't go to battery life, it'll go to higher performance, more screen brightness, additional sensors, more allowed background processing by apps, more GPS check-ins, more chatting with your connected devices like the Watch, and more awareness of the radio-transmitting devices around you. There's a LOT more our phones could be doing if they had 2x, 3x, 10x battery life, that would eat up every bit of juice within a typical day.