I was able to install this plugin but never able to get the email notification working - see my earlier post on this topic.
For example, I disconnected the UPS from utility power, and the plugin detected the Mac was on battery, but there was no notification by email of the event.
If you are able to figure this out let me know.
Indigo can detect a power failure on the USB interface device (since it is plugged in to an outlet) and send an email on that, and the Power settings on the Mac will shut down the Mac when the UPS gets low. Getting an email on low power UPS would be nice also.