The batteries appeared to have failed on this APC SmartUPS-3000 I use to run a server rack. Fine, I order new batteries, they show up, install them, I run a battery calibration and it shuts down after 2 minutes. I'm running about 20% load (approx 600 VA), it should run for over an hour. It thinks I have 4 minutes total of capacity. So I think one of the new batteries must be bad. I rig up a load tester and run them at 3A, there's a little variation, but the worst is still roughly 15AH.
So, maybe it only shows up under load. I put them back in the UPS and monitor the battery voltages and current during a calibration run. One battery looks a little iffy, but the discharge curves are looking fine (see attached) At then end of 140 seconds the UPS thinks I only have 2 minutes left. Now I'm wondering if the monitoring circuitry in the UPS went squirelly. Or is that one battery really that bad? Anyone have any idea what to look for?
These are 12V 18AH AGM batteries