iPhone 4 4S Battery Back Up Power Chargers Case MUZE&reg; 4000mah Case Charging Extended Battery Case Slim Power Pack Case Rechargeable Case within Built-in Video Kick stand Retail Packaging (Black/1pcs) Built-in iPhone 4 4S 4G 4000mAh high capacity rechargeable Li-Ion battery case Light-weight, super-slim design to provide power for your iPhone 4 4S 4G Fully charged in 3-4 hours, 4 Led lights indicates the power level Can also work as a protective case,battery itself charged through USB port or USB charging adapter Compact and lightweight, you can use your iPhone as usual as you use this external battery