Is that actually an UPS or just a backup battery? Can it passthrough the line power directly or does the inverter need to run 24/7?

In the latter case you might want to check how much power the inverter eats just by itself. For example, my Bluetti with 2 kWh needs a whopping 50W in idle just to keep the AC ports powered. Of course your unit looks much smaller so it should be way less but still worth measuring.