APC SUA3000 On Battery beeping/flashing, but it still working steadly for HOURS at 30% load ??

[Anonymous user]

My APC SUA3000 120v. It is acting strangely. On battery power, with a variable load of 16 to 33% and after 3 ~ 5 minutes with the 5 LEDs on (Battery Charge Indicators) it begins to beeping and flashing while go down very quickly until only the lower LED is on and still beeping.
After that, the unit continues beeping/led flashing, but supplying stable backup power without failures or interruptions for sometimes up to an hour and a half, once it reached an hour 45 minutes! 

It's not that I'm not happy with such "amazing" performance, but it's not realistic and not compliant the runtime table specifications for this model, also the cont. beeping is becomeing a CIA torture!
The UPS finally shutdown, after an mean of 80 min. +/- of perfect backup power.

AFAIK, beeping/flashing indicates that "...the UPS has reached a Low Battery condition and will soon shutdown. The UPS can only operate on battery for a limited amount of time.."  which I read is around of 2 to 10 minutes, upon configuration.  ( I don't use Power Chute or similar, just manual from the front unit panel)

Some facts:

- The batteries are new and charged 100%  but this also is happening with a 1 year old set of batteries I have as backup.
-  When I turn on the ups with the utility power re-established, the battery indicator is on TWO leds (24%) .
- I did a manual runtime calibration for each battery set, but nothing change, the UPS still running weird long runtimes and beeping.
-  The 16 to 33% of load is measured and calculated around a min of 850 wats and max of 1200 wats for:   4 core/8 GB RAM desktop PC two 22" monitors, Laptop Intel i3 17" 8 RAM, sort of pro usual audio recording studio equipment like mixer, monitors, amps, synth keyboard MIDI controllers, efx racks, 4 2TB external hard drives, ethernet/WI-FI 300 bp modem/router.
I am trying to figure out what to do, I fear that the unit or the batteries or both suffer some damage.