I may be wrong, but 2 of the 4 cables in USB are for power, +5v and -5V.
it *SHOULD* just be a matter of putting a meter to the cable while plugged into a USB port to find out which pin is which, then splicing a USB cable to a 6V(or step it down to 5V) SLA or whatever else you wish to power it with.
of course, this is only practicle if the unit can operate standalone, ala digi-mod UA5(forgoing power req)