backup battery and protective case in one. The offGRIDâ„¢ Backup Battery Case for iPhone 4 is the thinnest, lightest and most efficient iPhone backup battery case available. This ultra thin rechargeable battery built inside a snug-fitting, low-profile protective case promises to double the battery life of your iPhone 4. Simply plug in the included micro-USB cord to store the power, unplug at full charge, and enjoy longer life.