sequential flashing lights on SURTD5000

[Anonymous user]

Hi,
i have a problem with my APC UPS. its a SURTD5000VA rackmount 3U. symptoms.
1. when i first power up. online light and battery light (60% batt) is on. i am able to power my appliance (low power)
2. when i press and hold the PWR on/Test button, it is able to do a diagnostics no prob.
3. at this load condition (about 200w), according to the serial connection to my laptop, i am able to off the mains and the appliance continue being supplied power.
4. i increase the appliance power (about 1700w), here, 2 load lights lit up. when i off the mains, the lights start lighting up and turning off sequentially from up to down and back up again (i.e. the online and overload lights up together, then offs, then the batt and fault lights up together, then off, then the bypass and replace bat lights up together, then off, then the batt and fault lights up together again, then back up and down. etc etc. ). and the appliance stop being supplied power.
5. at the above load point (1700w), by input voltage to the UPS is 233VAC and 50Hz and output from UPS is 230VAC and 50Hz, as seen on HyperTerm via serial from UPS.

what is the problem? Appreciate your help pls.