The Sony a7s is notorious for it's terrible battery life, given the tiny battery that the camera uses. This is the solution for all-day power.

The Switronix PowerBase is a power solution that adapts a v-mount battery to be used with camera systems without a v-mount connection. This particular set is for the Sony a7s or a7r.

This includes a battery, quick-release plate, power adapter for the camera, and a charger.

The PowerBase features three p-tap outlets for powering accessories and/or charging.

For more info: http://www.bhphotovideo.com/c/product/1077507-REG/switronix_pb70_a7s_powerbase_70_battery_for.html