Having three wires seems to just be the way it is hooked up in the case of the Wallstreet. IDK about older PBs. Pull the heatshrink and/or sticker off to have a look.

Someone with a spot welder could whip these things up really easily. Having a PB PRAM/backup battery database might be a nice start.

RE: permanency.

I do not think you are going to easily find a way for that. Unless you ripped off the PRAM and wired up an interface to something non-volatile.