New idea maybe? Zigbee/Z-Wave enabled Battery UPS?

I’m a little confused about what you’re imagining, but there are certainly people who get to the same end result, which is a notification that the power is out. You just have a regular UPS and you have your smartthings hub and router on that. and then you have another device which would notify you that the mains power was out and it had switched over to battery power. There are devices you can buy, or you can make your own.

There are about a dozen threads on this already, here’s one example: