Not sure about the 6a but I've done it for the 10a. The 10a is a 36 volt so we used 3 12v shop batteries fed into a wiring harness that put them in series to produce 36v.
There was an article by Jeff Jackson published in Climbing Mag (or was it R&I?) a while back explaining how this is done-including diagrams. I'll see if I can track down the specific issue for you.
Thanks for the input Ed. I would love to breath some life back into her. The tool itself runs great, it is just the battery and charger that went to hell.