As the power grid has grown more unstable here, I have quite a few UPS's here and needed to determine when to replace the batteries. The linked URL has a YouTube video detailing the process. In short, these are the steps:
Remove the battery from the UPS
Connect the battery tester and make the following selections:
Out Of Vehicle
AGM Flat Plate
CA (Set to lowest possible - 100)
Record the Internal Resistance
Site to order quality, reasonably priced replacement batteries: https://www.upsbatterycenter.com/