Question about low cost backup network

Hi guys,

I am in a rather unusual situation. I am trying to make my network resilient to power outages (which are frequent), but my network gear uses too much power for a battery backup to be cost efficient for me (just take my word for it).

So the plan is to have a separate router attached to a small battery, but this doesn’t seem like a common setup at all lol. My understanding is that if I put a switch between the WAN connection and the router, that it should be ok so long as nothing else is plugged in. Is that correct? ie I can have both routers plugged into the WAN via a switch and it won’t cause problems so long as they aren’t both on at the same time? This is a PPPoE fibre connection.

Ideally I’d like a way to have the backup network automatically switch over in the event of a power cut. If you have any advice for how to set that up please let me know. I was thinking about using a micro-controller with a battery, similar to some commercial solutions that I have seen. I am not interested in the SMS notification style though.

Any advice appreciated.