I’m doing that. Works fine. There’s an article in PMOS wiki about limiting the max battery voltage.

Syncthing? git-annex?

My current router is an ancient laptop running NixOS. Ethernet in via the Ethernet port, and out via a USB converter. It probably could serve as a WiFi AP too, but currently I have a dumb OpenWRT in bridge mode for that.

The same laptop also selfhosts Prosody, coturn, LiveKit and stuff.

I don’t really see how a proper router would be better than that.