UPS battery backup died silently and took two switches down with it

Last Tuesday at our office in Columbus, the power flickered during a storm and my APC unit just quit. No beep, no alarm, nothing. Two Cisco switches lost power and the network was down for almost an hour before I got there. I checked the battery log and it showed no faults. That thing was only 3 years old. I replaced it with a LiFePO4 unit this time. Has anyone else had a UPS fail without any warning signs? What do you use to monitor battery health?

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hugo_jones25d ago

Three years on the original battery is actually pretty normal life for a sealed lead acid unit, and the failure mode you saw is the common one. The battery logs on most consumer APC units only catch slow declines, not the sudden cell death that happens when a plate shorts out internally, so a clean log does not mean much. That is why I run a cheap network card in mine and check the self test history, plus I do a pull the plug test every six months to see if it actually holds. If you want real warning you need something that watches the battery voltage curve over time, not just the alarm status, because the alarm only fires after the thing is already useless. So I would not call it a silent failure so much as a limit of what that class of unit can tell you.

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