Preview at WWDC likely in June, followed by September launch.
Next Generation iPhone Battery Only Marginally Higher Capacity
Part photos of the new battery for the next generation iPhone have been posted by 9to5Mac. The part shows only a minor increase in capacity from 3.7V/1430mAh/5.3Whr in the iPhone 4S to 3.8V/1440mAh/5.45Whr in the rumored iPhone 5. No dimensions are provided to compare the size of the battery to the current iPhone batteries.
The next generation iPhone is believed to be a taller but thinner device. The increased height, however, is more than offset by the reduction in thickness which results in a decreased internal volume of the device as compared to the iPhone 4 and 4S. If this part leak is to believed, Apple hasn't been able to significantly increase the battery capacity on the new iPhone.
The new iPhone is expected to include LTE data networking for the first time. LTE has traditionally required more power than the currently supported 3G networks. Apple's Tim Cook has said that the reason that Apple hadn't used LTE in iPhones is due to the "design compromises" required to build such a device. This has widely believed to have referred to the increased power requirement of existing LTE chips. Qualcomm is poised to release a new LTE chip that Anandtech believes will "likely increase LTE battery life to reasonable levels".