Despite the iPhone 4’s increased battery life, if you need more juice, Energizer has just begun shipping its AP1201 case for the iPhone 4 that offers a built-in li-ion battery pack that promises to nearly double the battery life of the device. LED lights on the back of the case are capable of indicating the battery life of the case and it can be recharged 500 times thanks to its own USB charging cable. Users will be able to charge the case and the iPhone 4 separately, or at the same time via a pass-through charger. The case is made of recycled silicone rubber and has an integrated bumper that claims to be able to eliminate the signal degradation issue. The Energizer AP1201 will set you back $70, which shouldn’t break the bank.