[kop316]

Re-reading I was thinking the same thing. Batteries don't just "die", they degrade in performance.

How did he also know power didn't go out too? That confused me as well.

[danilocesar]

because he gets emails from the unit when it happens.

I had a script in a raspberry pooling my UPS each minute asking if the unit was running on AC or battery, and dropping that info into a file when it changed. I know the software/daemon can also do something like that.

[jaywalk]

Yes, but in this case he wouldn't have gotten an email since the UPS failed right when the power went out.

I actually had the exact same thing happen to me a few months ago. A power flicker so brief that it didn't even reset any of my clocks, but it caused one of my cheapo standby UPSes to give out.

[monoideism]

Probably he knew because none of his other electrical appliances were reset.