Heavy users always need a battery pack for their iPhone 5 as the battery juice will usually not last more than a day. Mophie has recently expanded its line, and added the Mophie Juice Pack Helium which is specially designed for the iPhone 5.
The new Helium iPhone 5 case is said to be 13% thinner than previous iPhone juice packs. The pack comes with a 1,500mAH battery which doubles the usage time of your iPhone 5. This allows you to have additional 6 hours of talk time on 3G, additional 6 hours on Internet or LTE and additional 7 hours of video playback.
The Juice Pack Helium is rechargeable via USB port, and comes with a microUSB cable. You can charge the Helium case and your iPhone 5 at the same time. There is an LED indicator which shows you battery level easily. A dark metallic model of the Helium Juice pack to come in February, while a silver model is slated to come in March. For a price of $80, you can get it here.