I'd start with whatever web presence the UPS brand you didn't mention has.
Yeah, I suppose I should have mentioned that. It's a Liebert (later Emerson, now Vertiv) UPStation GXT2000RT-120. This line of UPSes has been discontinued for quite a long time and the brand has changed hands twice during that time, so I'm doubtful the company would be of much help. They'd probably suggest buying one of their new (and expensive) GXT4 series models

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Looks like an MGE or Liebert battery bay shorting connector.
You hit the nail on the head; what I am specifically looking for is the battery shorting connector (connects the two 48 V strands in series to get 96 V after you have installed the battery assembly and are less prone to shorting or accidentally touching the 96 V). But I can build one of those if I can get ahold of the right connectors.
The dc plugs are Wellshin http://www.wellshin.com.tw/en/m/
eg. Sockets
45 amp EM-022
25 amp EM-009
Perfect, thanks - that's exactly what I needed! Much appreciated!