Here's an overview of the new Switronix PocketBase power solution for the BlackMagic Pocket Cinema Camera that runs from common and affordable Canon LP-E6 batteries.
Though it is functional and probably the most affordable off-the-shelf power solution for the BMPC (currently), I can't say that it has all it's bells & whistles in place. The LP-E6 batteries don't have an actual lock, which might be a concern when running around with a BMPC in hand.
In order to get to your SD Card, you'll need to get the camera off the PocketBase by first removing the left side battery to access the unusual thumb screw. I think anyone using this will quickly add some type of QR system. If all of this is too cumbersome, at least the entire PocketBase can be relocated a short distance from the BMPC with the provided long cable.