There are also BMCC-specific external power solutions from IDX, Anton-Bauer, Hawk-Woods, IKAN, and many others. Some are of the V-lock variety, others use AB-type 3-stud mounts, others use Canon or Sony compact camcorder batteries, and others.
Some batteries feature strong attachment systems with flexible designs to make it easy & quick to attach/detach the battery to your camera or rig. To a certain extent this comes down to personal preference -- choose a battery system that works the way you like.
In general, lithium-ion batteries weigh significantly less per watt-hour of capacity compared to nickel-metal hydride batteries. LI batts tend to be more expensive per watt-hour than Ni-MH, but both can be excellent values if made by reputable manufacturers.
Don't forget chargers: Some can be relatively expensive, and if so, be sure they have worthwhile features, such as fast charging times.
Search your favorite video dealer's website and the web. Lots of choices.
I recommend against buying from a no-name supplier or least-cost eBay source. An incorrectly wired external power cable or battery system can damage your camera. Better to go with trusted brands and dealers.
I use the Switronix BMC Jetpack. It's expensive but it gives full power distribution to everything on your rig. It really is a life saver. It also has helped breath new life into my HPX170 which I now use on small shoots or sizzle reels with a hyperdeck shuttle. The Jetpack's power cable for the camera powers the hyperdeck and Switronix makes a 7.2V LEMO to Panasonic CGR battery adapter. When both the BMCC or the Panasonic rigs are built up, it's excellent.
Of course, this makes sense if you have V-Mount or 3 stud batteries already or if you want to get into them. But you go all day on two bricks.
Blackmagic Cinema Camera, RED Scarlet-X, Panasonic HPX170, Canon 7D
2011 Macbook Pro 17", 2.3 Ghz Quad Core, 16GB RAM
Adobe Production Premium CS6, Avid Symphony 6, Final Cut Pro Studio 3
The College of William and Mary
Hi, I know this is an old post. Just wanted to add this option, which I use: http://amzn.com/B013KWVXI2 http://ecx.images-amazon.com/images/I/81xURP02fSL._SL1500_.jpg
It's a Juicebox battery specifically for the BMCC and was only $99. So far, it works great and I've already ordered a second for swapping purposes. Hope this helps anyone looking!
I second the Switronix Jet Pack. I have it for my BMCC (get the extension cable, as your particular configuration might require some extra length on the power cable). It powers multiple devices, including my wireless (2), Alphatron vf, and a Nanoflash.