The Case Relay Camera Power System from Tether Tools. Equipped with a built-in 7.4V, 1,200mAh lithium battery and a 5 VDC input via USB, this system will provide power, while being connected to an external power source for a nearly constant source. When connected to a 2A USB battery pack or an AC adapter, the Case Relay can still be able to provide a constant supply of power to your camera, and thanks to the internal battery the system will support hot-swapping of external power sources. An LED indicator light will shift from green to yellow to red to show battery percentage so that you will not accidentally lose power during a long time-lapse or video production. This system is compatible with numerous camera systems through the use of a separately available coupler. This coupler fits into the battery compartment of your camera and acts as a dummy battery to supply power.