Happy for thay person, but something doesn't addup. 4 fans load will be at least 30 Amps at 12v on good inverter. And can be upto 40 Amps on bad inverters.
AGS GX200 F is rated at 175 A.H. capacity.
With that much load, it shouldn't go beyond 6 hours i guess.
Worst case scenario, UPS is overcharging battery to 15v and then may be draining it all the way down to 7v. Hence great capacity but sure gonna kill the battery fast.
I am confident that my UPS can run 4 fans + lights for 12 hours but it has a pair of GX 200 F.
Also the Multimeter you are using in above post doesn't support DC Amps. It can check only AC amps and AC/DC voltages.
To check the DC amps between UPS and Batteries, you'll need something like this.