Slightly off-topic, but isn't it a bit sad that "an all-day battery" is considered a perk nowadays? There was a time (pre-smartphones) when you only had to charge your phone once per week, or even less. And while I am aware that the huge screens we now have and the apps we're using are battery hogs, sometimes it still feels like we've taken a step back.That $129 Moto E ($79 if you get a contract, which you shouldn’t) runs Android 4.4.2, sports a Gorilla Glass screen, has an all-day battery and is even water resistant.
More processing power is in high demand with mobile right now and efficiency necessarily is taking a back seat.
Look at Intel and x86. Computers have become fast enough for the average user and raw computing power is only increasing modestly each generation but the new 14nm chips are estimated to be 30% more energy efficient than the previous generation. At some point mobile will come to heavy battery life competition.
A step back? We need to accommodate for the leaps in technological innovation. The drive to make phones thin and smaller is also providing the incentive to improve on the battery.