SUA3000RMXL3U -- "replace battery" blink and slow beep

[Javik_apc]

What does it mean when "replace battery" blinks and the UPS makes a slow beep about once a second?

Something went wrong today and the UPS dropped load, turned on and after about 30 sec dropped load again, etc. Had to pull it out of service.

After letting it recharge and then pulling the plug on it with no loads, it depleted the charge in about 5 minutes.

When plugged back in, the charge level bar which was at two lights, blanks out, and then replace battery starts blinking along with the slow chirp.... chirp..... chirp....

Online docs say this means the battery is detected as not connected and needs to be plugged in. It is plugged in. I unplugged and reseated the cord, and it still does this chirping.

I assume this is either hardware failure or a battery that is way too weak to be useful anymore. The UPS is out of warranty and we are replacing it, but I am interested to know about the slow beeping.