There were rumours that iPhone 6 will have a much powerful battery than the previous iPhone. The latest leaked images on a Chinese website has suggested those rumours maybe true.
This looks completely logical that Apple will come up with a bigger and better battery in iPhone because the new iPhone has a much bigger screen and higher resolutions then the previous iPhone.
The battery size will be around 5.5 inches and capacity of 2,915 mAh. The Phone will be launched on sept 9 but it looks unlikely that the phone will be available in the stores in Sept. The Apple is facing some production issues regarding their iPhone 6. It looks like that iPhone will be available in markets from November.