The Switronix Powerbase-70 Battery Pack & Charger for Blackmagic Camera Kit from B&H -- the battery can be attached right underneath the camera or to a V-mount plate and will provide up to 4-6 hours of power. The charger delivers a full charge in 4-5 hours using a P-Tap connector.
The battery pack is a combination of a 70Wh 14.8V lithium-ion V-mount battery and a regulator block with a 12 inch DC cable. The battery attaches underneath the camera via an included mini quick release plate that has a 1/4"-20 screw extending from it. The plate snaps into the battery and enables mounting most any support gear with a 1/4"-20 thread. If you'll be attaching underneath the camera, you'll need to plug the 12 inch DC cable into the camera. If you'll be attaching to a V-mount plate, you won't need to use the cable as the battery is a standard V-mount battery and accordingly will make electrical contact with the plate. The battery has 1/4"-20 threads on the sides for attaching accessories.
Via an optional XP power regulation cable, the battery can also power two additional 12V and lower-voltage devices at the same time as powering the camera.