How can I get the data from APC UPS into OpenWRT, to shut down the router if the UPS battery is low?
https://www.apc.com/shop/pk/en/prod...x-IEC-C13-outlets-SmartSlot-AVR-LCD/P-SMT750I
it does mentions
Network manageable via serial, USB or optional ethernet
Is there a package for UPSnuts or something?
There's a nut package
There is also apcupsd. Not as comprehensive as the nut package but a lot lower learning curve.
I can initiate a shutdown on the mains powered desktops, and any devices running on self contained battery power have that capability built in, so it does what I need it to do.
screenshots are always welcome.
@frollic Is that nut package not a Nutcase? 
Do we have to follow this guide to your screenshots?
Pretty much, though I've customized the alert scripts to my particular use.
Nut the package will create a NUT server? bcz Homeassistant NUT integration pulls data from NUT server
The Network UPS Tools (NUT) integration allows you to monitor a UPS (battery backup) by using data from a NUT server.
as always here is a few Youtube videos on the topic
