Wouldn't mechanical recharging make him a perpetual-motion machine? It was mentioned that he does recharge by moving, in "Birthright" IIRC, but that would just increase the efficiency of his power usage. His primary power source wasn't discussed in the canon.
I thought maybe he was wirelessly connected to the ship's power grid, and had batteries for use off ship, or away from any external power grid. I wonder how long that could last, though. How long was he stranded on that medieval planet in "Thine Own Self"?