You are most likely still protected, however the "Back-UPS" units are usually more intended for small, lower power devices like your router or cordless phone.
While they can be connected to computers, the information they output over USB to the host is usually only "core" information about line conditions, battery voltage and estimated runtime.
I believe the error you're getting means that either the ACPUPS service, or the UPS itself attempted to perform a self test (I believe APC UPS's perform self tests every 2 weeks), but that your UPS doesnt support reporting on it.
It may be possible to perform one manually, however I would recommend stopping any Containers or VM's if you have them running and then stop the array (just in case) first, then try holding down the power button on the UPS for around 3 seconds. The power button should begin to flash and then go back to solid once the test is done.
You can also try just unplugging the UPS from the wall and see if it holds.
If it does, i'd recommend leaving it unplugged and letting it drain to around 30%. This should help re-calibrate the UPS's estimated runtime.
It's also a good way to test if notifications (assuming you've configured a notification agent under `Settings => Notifications`) are working properly