why not build your own much more flexible. shouldn’t be very hard. just get a battery like this one www.amazon.com/…/B094NN5KWY and an inverter.
i have had terrible experiences with these all in one UPSs that you mentioned, battery degrades fast and starts lasting only a fraction of the time. i would suggest getting a killawatt to measure power consumption, gives you a much better idea of what capacity inverter you need.
I’m looking for something that is rack mountable and 2U in height. While it is possible to find off the shelf gear you can build your own out of, it isn’t cheap.