I have 5 300 VA units, 2x cheap brand, 2x CyberPower, 1x Eaton.
I think 2 of them don’t have a transformer.
Does it matter? All have a 9 Ah 12 V battery.
It will last few to 20 minutes maybe.
No issues so far (battery capacity loss excluded).
Recently, as someone recommends, all batteries are outside of UPS enclosure,
lower temperature. Which could affect battery lifetime.
More power, more money 👀
I will not recommend it if you don’t have enough experience.
Fire hazard.