"Infinite Power for Your Camera Relay Camera Couplers from Tether Tools work in tandem with the Case Relay Camera Power System (CPS) to keep your camera powered continually with an external 5V USB battery pack or wall power. Relay provides peace of mind knowing you have an uninterrupted power source for your camera. When you're ready to get powered up, simply insert the Relay Camera Coupler directly into the camera battery port. Then attach the Relay Camera Coupler to the Case Relay CPS (sold separately) and power your camera with any standard 5V USB external battery or an AC power source, such as a wall outlet or generator. The Relay Camera Coupler combined with the Case Relay Camera Power System provides constant, uninterruptable power for your camera and is perfect for time-lapse photography, photo booths, video production and power-hungry LiveView shooting or any long day on the set. Relay Camera Coupler and Relay CPS Benefits: More cost effective than purchasing multiple proprietary camera batteries. Power sources are non-proprietary. Power your camera with the same 5V battery you use to charge phones or tablets. Never need to charge camera batteries again. And never run out power. Compatible with most Panasonic DMC-GH3, DMC-GH4 Camera. A Case Relay Camera Power System (sold separately) is required to use the Relay Camera Coupler"