i am surprised the APC even works without a proper ground circuit! most
will fail to start when ungrounded.

Sorry but you are incorrect. I have used various APC UPS models from a
smart-ups 300 to a 1500, an old APC power cell model, and also APC Back-UPS
1200 and a Back-ups pro 500 without a ground. All of these models will
function without a ground.