iPowerCase 1500 mAh Li-Polymer Rechargeable Battery for iPhone 4 (Black) Capacity: 1,500 mAh - Provides additional 5.5 hours of talk time (on 3G), 6 hours of internet usage time (on 3G) Charge and sync iPhone 4 with iTunes without removing it from the Power Pack Smart battery technology drains battery of the Power Pack first before switching to the iPhone's battery Convenient rechargeable battery allowing you to always have a battery charging backup when you are away from an AC outlet