NTK iPhone 4 4S 4G External Solar Powered Battery Charger Case With Extra USB Power Outlet Juice Pack 2400 mAh Solar Powered iPhone 4 Charger Case, Extra USB Power Outlet Enable Charging to Your Other Mobile Device Such as HTC, Motorla, Blackberry, Samsung... 2400 mAh smart Lion-polymer Battery Slip-in Design with Anti-Slip Edge On/off Button to turn charging function on/off 4 Led Lights indicates Power level remaining in the case