The iPhone 5 is supposed to be an 4G LTE phone. LTE requires a lot of energy so the battery needs to have a bigger capacity to reach 3G talk times. Apple is known to focus on extending battery life. Apple never wants to release a new product with less battery time than the previous model.
9to5Mac published photos of what is supposed to be the iPhone 5 battery. The capacity only increased from 1430 to 1440 mAh compared to the iPhone 4S. Unless Apple found a way to implement LTE with low power consumption, we will net see LTE in the iPhone 5.
The new iPhone 5 is expected to be announced on September 12th. The iPhone 5 sales are then to begin September 21st. Rumored features of the new iPhone 5 include a larger screen, A6 CPU, iOS 6, small dock connector, 4G LTE and NFC. The overall design would not change dramatically, only the backside material is not glass anymore. More iPhone 5 Rumors.