Battery in back = to power the back, so that the energy is lot comming from the computer/firewire, as via the TB connection you can't get enough power, its just to transfer images..
Just try it out: Take a Loaded battery for your image bank, click it into the imagebanl, then setup everything as you would shoot without computer, next step : connect imagebank(with battery) running to your computer via TB, and start phocus, or flexcolor, should work.
If not, try the powered firewire repeater fitst, its cheaper than the bluewave bank..
Otherwise google Bluewave imagebank ...