Uninterruptible Power Supply Unit Failure, Or Is It the Battery?

[Anonymous user]

I have a SUA750 Model UPS unit that has been in service since late 2008. Recently, it failed completely when there was no power outage. (If any power outage occurred, it was only for a small fraction of a second.)

The unit interrupted the power supply to my PC equipment momentarily, then restored power again, but the "replace battery" light came on.

The problem is, the battery in the unit is less than 2 years old and is a genuine APC brand battery purchased directly from APC. It has been passing the "check battery" test with no problem every 2 weeks ever since it's been installed.

How could it be that, all of the sudden, the battery can't supply backup power for even a fraction of a second, when it's been passing the "check battery" test every time it runs? (The load on the UPS unit is only 20% of it's capacity.)

I power-cycled the unit and ran the self-test, but the "replace battery" light remains on.

Could it be that something is wrong with my UPS unit? I only ask this because it seems strange that, in less than 2 weeks time, the battery went from being able to power my PC equipment for at least 8-10 seconds during the regularly scheduled battery test to not even being able to power it for a fraction of a second during a blink outage... Perhaps the unit itself is malfunctioning?

[Anonymous user]

Have you tried recalibrating the battery?

[Anonymous user · Accepted solution]

How do you recalibrate the battery? -- So far I tried turning the UPS off and performing the "brain dead" test to check the internal circuit, and I also performed a manual "self-test" on the battery. -- I'm not sure how to recalibrate the battery, though. Please explain...

[voidstar_apc]

Calibration might help if the battery works well but the UPS predicts poor runtime, but that doesn't seem to be the case here -- the UPS indicates the battery is bad after it couldn't keep the load powered. If you have another 750VA UPS, you could try swapping batteries and see if the problem follows the battery.

[Anonymous user]

I don't have another 720VA unit, unfortunately.  I think the capacitors in the UPS are bad because this thing failed when there was no power outage. It might have went to trim or boost power and tried to use the battery when something electrical in the unit failed.  I don't think the battery is bad yet.

[voidstar_apc]

The UPS goes to battery when switching to/from boost or trim. It's certainly possible something inside the UPS has failed rather than the battery, but I don't know of a good way to distinguish the two without another battery or a power supply acting as a battery.

[Anonymous user]

Thank you for that info.  I'm going to buy a voltmeter to test the battery and see how many volts it puts out.  That should answer this question, I think.