Before the “whole house backup” with my victron system i used this ups and had my NAS, homey and all the ubiquity networking stuff behind it. It a cheap and good ups. Paid around €120 for it.
@Peter_Kawa Homey works offline if your sensors work also.
@StefanA I wouldn’t bother with a mobile router. It makes things almost impossible to connect/use.
Perhaps you can get a good quality router UPS such as this. They are quite famous and easy to find in India for many reasons 
. Most popular models output 12V and you need 5.2V, so you can use a cheap DC-DC buck converter modules based on LM2596 to drop the voltage. Since it is buck converter, the efficiency should ideally by greater 90%. You can also get one with a screen such as this so that it easier monitor and maintain the output voltage. I know the links point to Indian shops but I am sure you will be able to find same or similar components in your home country.
I also use my Homey as my home security.
The Homey2023 is on a powerbank with passthrough charging.
My ASUS router is on an APC UPS, with a USB 4G-card connected.
So on power outage the Homey and the router will continue for a while, and the router will failover to 4G for notifications like water/smoke sensors or burglers.
Maybe this could be a solution, if you dare to open up the Homey2023.
Homey’s PCB doesn’t have exposed GPIO pins, so that hat won’t work.
Darn
