>>I don't see how a UPS could "backfire."
>
>UPSs use gel-cell lead-acid batteries, which have a maximum life of ~5 years, and their capacity can be significantly diminished earlier than that. They need to be tested regularly to ensure they can provide the required uptime under load.
>
>Also, the control electronics in the UPS can fail.
>
>Over the years I've had quite a few client UPS batteries die, and 2 cases of failed UPS electronics. However I'm completely convinced that in every case my clients have more than recovered UPS replacement/repair costs in increased longevity and reliability of downstream equipment.

I see how a UPS could fail, but how can it "backfire" as someone suggested?

Tamar