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 lost excluded).

Recently, as someone recommends, all batteries are outside of UPS enclosure,
lower temperature. Which could affect battery lifetime.

More power, more money 👀