APC UPS STATUS ONLINE LOWBATT

For at couple of years I've had an APC Back-UPS CS 500. Recently it started to report ONLINE LOWBATT and TIMELEFT decreased dramatically. Originally it could run several minutes on batteries without powering down, but not anymore. Just a slight glitch in power and the apcupds would power down the server. This weekend I got a replacement battery from APC, but the problem persists.

I tried contacting APC support which quickly responded with a document describing a manual runtime calibration. The manual runtime calibration consists of running on at least 30% load, batteries 100% charged, yank power and let it run until it dies. It took around 21 minutes on 34% load which is fine, but after a recharge apcaccess still lists TIMELEFT 0.8 minutes.

APC support was not suprisingly less responsive when they got to know that I was using apcupds.

A bit more suprising is the informative APCUPSD User Manual, which states at least 40% load for the "soft" runtime calibration. I was using the "manual" runtime calibration which only states 30%.

The only apparent option left is to reset the UPS battery constant, however it seems to be unsupported on the Back-UPS CS series. Alternatively I could perhaps try another "manual" runtime calibration with 40% load as suggested for the "soft" runtime calibration...