I had an idea it's configurable in its admin-panel, but it may not. Please check the following:

So, to conclude: the official documentation is right. Hot-swappable or not, the UPS cannot boot without at least a bit of charge in the batteries. That's all it requires to come back online — and start to fully charge the batteries. I did not experiment to see if, after having booted, I could remove the batteries at will and put them back in again, with the UPS automatically managing the switch to AC power. So that question remains unanswered.

The problem, in your case (as well as on mine) is that the batteries have to be installed first before you know if the motherboard is fine or not.

Source

Super confused about the situation here. You bought a UPS without batteries? I would assume the side marked for batteries+surge would not operate properly if no batteries were present if this model isn't hot-swappable.

Edit: the product page says this unit should be hot-swappable, BUT, it may require the batteriesnto be present first in order to engage the PDU to turn on power to each individual outlet, so mayyyybe getting batteries would make it work, but who knows.