Of course one must be careful with polarity. IS the plug the same as the MTH? I am out of town so I can't compare. If it is, may be the wires can be eased out and switched around if the polarity is reversed.
The photo was squeezed when copied so it looks like they are long. but I think they are the same size as the MTH which I believe are standard 1.2V nimh size.
BTW, it is advertised as a 1.6WH and 660 MAH so I think the charge circuitry of the MTH should suffice.