The Battery Pack is only necessary if your airplane does not have a VOX style intercom or if you want to use your Standard or Amplified SafetyCell outside of the airplane. A lot of users like to use the SafetyCell in high noise areas like factory floors, trucking, riding lawn mowers, tractors, boats or any place where you need protection from noise and want to have a clear and quiet cell phone conversation. If you have chosen one of the Battery Powered SafetyCells, you do not need a battery pack.