small office UPS replacement

just a short over-the-shoulder look at me on an assignment replacing a dead UPS in a small satellite (branch) office.
Uninterruptible power supplies can be tricky to deal with because they are so heavy. They are essentially a bunch of lead batteries in a metal box.
In this video, I run into a snag where the replacement I install doesn't seem to be working correctly. But, turns out there was a logical explanation.