Yes, the TSU6000 also has three wires. The white and black wires both attach to the negitive terminal (on MY remote, I don't have the original battery pack any longer, but I'm looking at my remote and that is how I have mine wired, no ill effects after a year). While I do not KNOW, I do suspect that one contact is used to supply power from the battery to the pronto while the other wire is used for charging the battery. This would allow protection to the pronto when supplying a higher voltage to the battery during charge. That makes sense to me, but I do not know that's what it actually does. I do know that there was voltage present on all three wires of the original battery.
Hope this helps.