The MOV-303-2204 Dummy Battery Power Cable from Movcam features a dummy battery at one end, and terminates in a D-tap connector at the other. The cable has a voltage capacity of 8.4 VDC, which allows you to power your Sony a7S camera by plugging the cable's D-tap connector into the D-tap outlet of either a V-mount or a Gold-mount battery.
Movcam MOV-303-2204 Specs
Camera: Sony a7S
Batteries: V-mount and Gold-mount batteries with D-tap outlets