APC BE750BB UPS 750VA Cicks, Buzzes, then Shuts off all Outlets connected to Battery Power

[TurbineTester]

As title says, i have a 750BB UPS and have had a few power outages lately as we have been installing line level equipment converting a property to solar/battery/grid assist.  Currently only have a PC and small peripherals connected to the battery backup outlets including cable modem, router(no-wifi), NAS, and one PC, no monitors or printers.  Yesterday during basic PC use, UPS clicked then buzzed and then turned off all outlets connected to the battery backup side of the UPS.  After unplugging things one by one to see if one of them was suddenly causing a high amp load, it was discovered that the battery backup side would click buzz and then disconnect even with no loads connected or plugged in to that side.  Currently everything is now connected to the "Surge Only" side and running fine.  I removed the battery and it tests just fine at 13.36v.  I feel the unit has performed pretty well for us the last ~10 years and it may be just nearing the end of it's useful life.  That being said, what else can i test or replace on the UPS?  I have no problem taking this thing apart and soldering in a new capacitor/relay if need be and it can be obtained economically.  Thank you in advance for any help.

[JonPro]

From the description that you have provided @TurbineTester, it appears that there is an internal hardware failure on the unit already and would recommend replacing the unit.