With all the hoopla around Apple and its newly outed iPhone 5s and iPhone 5c, the eagle-eyed among you may have noticed one particular omission from the specs list that we provided – the battery size. This is because Apple traditionally doesn't disclose the exact capacity of the Li-ion battery units that power the iDevices, for whatever reason. What Apple instead does, is it simply announces that the battery life of their new devices has been improved, compared to their respective predecessor, without getting into details.
Fortunately, there's a way around, and the folks behind AnandTech have extrapolated the battery capacity of both the iPhone 5s and iPhone 5c from their respective FCC listings, using a simple formula. So we now have a pretty accurate info on the exact size of the batteries: a 1570mAh battery for the iPhone 5s and 1508mAh for the iPhone 5c. Compared with the iPhone 5's 1440mAh unit, that gives us an increase of 9% in the case of the iPhone 5s, and a more frugal 4.7%, as far as the iPhone 5c is concerned.
To put the above in perspective, the battery on the Samsung Galaxy S4 went up 24% (2100mAh → 2600mAh), compared with the S3, while Sony Z1's went up an even more impressive 29% (2330mAh → 3000mAh). Having said that, do keep in mind that battery size isn't directly proportional to longevity – while the batteries on the new iPhones appear tiny next to the above, the latter is far less power-hungry, both because of the software and hardware.
source: FCC via AnandTech