Short beep every 9 minutes when UPS is switched off and powered off

[BillP]

For my home office (I am telecommuting), I recently installed a "Smart-UPS 700" (the label says the model is "SU700INET"). I had bought it second-hand and then got new batteries for it (2* 12 V, 7.2 Ah).

It supplies power to a medium PC and a 19" TFT (no gaming graphics), during operation only 2 of its 5 load indicator LEDs are lit; the batteries are fully loaded. I do not have any data connection to the PC, because I haven't found any software for that UPS model.

In the evening, I shut down my PC, then press the "0" button on the UPS, then switch off the outlet feeding it. After some time (not measured), it will emit a short beep every 9 minutes. It will stop if I switch on the outlet (mains power supply).

1) I didn't find that documented - what does it mean?

2) Is there any chance to silence the UPS (other than keeping it on mains power)?

3) Will constant power supply (versus switched off when powered down) have any positive or negative effect on the batteries?