If both PV battery walls and broadband CPE supported Power-Over-Ethernet as a backup power source, that would work too. POE supports greater distances than USB-C.
I'd prefer broadband CPE (UL listed) with a standardized backup power connector (doesn't exist, but I can dream). For DIYers, building their own magic box to convert from their powerwall to backup low-voltage small devices. This was one of the few DIYers who include appropriate fuses in their design. Too many Youtube DIYers treat low-voltage as harmless and don't include safety devices. I've seen the after-effects of a few DC/Inverter plant meltdowns. When I used to visit IXPs and data centers, all of them seemed to have at least one melted, metal wrench :-) https://www.youtube.com/watch?v=xsZzlF_NA6E https://projectswithdave.com/48v-to-12v-dc-dc-converter-project-build/