Apple spoke of increased battery capacities on its iPhone 5C and iPhone 5S smartphones. Wh (Watt-hour) values for batteries given out to the FCC by Apple, coupled with the nominal voltage of 3.8V, let Anandtech derive the capacities in mAh for the two devices' batteries.
The battery driving the iPhone 5S puts out 5.96 Wh, compared to 5.45 Wh on the iPhone 5, which works out to be 1,570 mAh, compared to 1,440 mAh on the iPhone 5. The one inside an iPhone 5C gives 5.73 Wh, or 1,507 mAh. Battery sizes alone don't determine battery life, several layers of power-management at the hardware- and software-level work toward that.