Analysts have suggested that a larger 4-inch display and LTE connectivity will require a bigger battery.
A series of photos posted by 9to5Mac reveal a battery which has a capacity of 1440mAH, while the iPhone 4 battery is 1420 mAh, and the iPhone 4S battery is 1430 mAh.
The voltage of the new battery is increased from 3.7 on the iPhone 4S to 3.8.
It also has a watts-per-hour measurement of 5.45, which is up from 5.3 on the previous model.
The display of the future iPhone is rumored to see an increase to 4-inches, at a resolution of 1,136 x 640, along with a two-tone back panel.