Recently I featured the Panasonic GH3 DC Coupler (seen here) used for running external battery power. Running external power is one way to swap batteries easily when the camera is mounted inside of a cage, or if you're looking to just have super long run times. If you're looking do the same for your Canon cameras, you can pick up the AC/DC adapter (as seen here) and slightly modify it, but you will still need to find the proper battery to run an optimal 7.4V DC.
Well here's a recent Portable Power Solution Product that offers a 6600mAh Portable Li-Ion Battery along with a dummy battery to provide long lasting run times for Canon DSLR cameras that run on LP-E6 or LP-E8 batteries. That should cover pretty much every Canon DSLR made in the last 3 years. Lanparte is a name that has been putting out quality stuff in recent years, and i'm hoping this is just as good. I have one on order now. Not too shabby on the price considering they state a full charge will be the equivalent to the run time of 4 batteries. Check out the portable power solution following the link (Click here).
Lanparte Li-On Portable External Battery