Aqara Smoke Detectors: Link/Group sirens across multiple hubs when offline? (M2 vs. M3)

I am from Romania but I live in Spain here all internet is fiber even outside the city there is fiber still you have an point there with the UPS I had 2 already for my iMac but doesn’t last for me first last 2 years and the second I think the same.so keep that in mind to see that if you spend some money on to see how long it will last till will be useless.