Apc Surt7500xlt Ups connections drawing - Powerware 9120 UPS System

The battery inside the APC is "weak", and the "beep" is telling you to replace the battery inside the APC, or, maybe cheaper, to buy a new APC.

UPS MOV is blown, change MOV or input filter circuit. or better send it to APC authorized service center.

First you need to get a APC serial cable from APC. Next connect it to a com port on your computer and the back of the APC. On your computer start Hyperterminal. Enter a file name. Anything will do. Slect your com port. Set the following setting to 2400 data bits and none for flow control. Leave the other setting as is. Hit enter twice and enter APC for user and APC for the password. The program will come up. From there it will be easy to set whatever you want. OH!!! make sure your UPS has a network card installed. If not you can't change anything.

how much current is your computer using?

First, you have the COMCAB which is an APC UPS communication cable ca. 2m length, for communication between APC UPS and PC/Server . Another type is the AP9870-BD.This extension cable for connecting hardware to a UPS up to 10 A, 2 m length, ident. APC AP9870.AP9875-BD Power cable used for connecting a UPS to the power grid up to 16 A, 2 m length, ident. APC AP9875. There are few other types of cables as well.

You could connect 2 computers with LCD monitors, but without a printer. The printer is a large consumer.
If you need further assistance, leave a comment. Cheers

You may be able to do this but it may NOT charge the external battery, you will have to see.... Anyway simply connect the battery up to the inside terminals Red- Red Black - Black.. with suitable wire & fittings make sure you have no shorts etc. ya good to go.

A UPS goes between the Power Socket and the PC equipment.
So ya can "Talk" to the UPS and change monitor settings. So do some don't depends wat ya want?
A "Smart" one is computer controlled, and most probably ya can "Talk" to it, the other is the "Vanilla" model, real plain.
More Complex.

Have you load tested the batteries? DCV is not a good enough test for the batteries, they could still open right up under load. If the UPS is over 3 years old, I'd swap the batteries. Your power is drawing solely from the batteries on AC line loss, so if the UPS is failing when that occurs, almost certainly is the batteries.

try plugging the pc directly into the wall...if it works the UPS is defective.  You can order new batteries for the UPS online.
Battery Planet.com