During the announcement of iPhone, Apple really wanted to point out that its iPhone 5C and iPhone 5S will boast longer battery life and although it was not clear whether it is software or hardware improvements, according to the post in Anandtech.com and some details of the FCC, the battery in the iPhone 5C and iPhone 5S are far more powerful and advanced than the prior iPhone mobiles.
The battery life is affected by using the wifi or wireless network or the applications running at the background. There must be some improvements which will reduce the background applications and running the applications and doing the processes in a faster way.
While all batteries operate at 3.8V, the main difference is their size. Although the Apple iPhone 5 is stuck with 5.45Wh or 1440 mAh battery, iPhone 5C has a somewhat higher 5.73Wh or 1507 mAh. iPhone 5S, with fast 64-bit SoC A7, it is even more battery with 5.96Wh or 1570 mAh.
The best part of this story is that Apple has managed to squeeze a much better battery life without compromising the size of the iPhone 5S, who managed to stay slim as the iPhone 5. iPhone 5C unfortunately not suffered the same fate, and in the end, it got a little thicker, but it was probably a result of the redesign of polycarbonate body.