Syncthing on Android has an option to only sync when on AC battery. The PC client might have a similar option. If not, you could probably configure something similar via systemd or udev under Linux.
I don’t think syncthing has proper means to synchronize contacts or anything else that’s not file-based though.
I use syncthing and prefer it for synchronizing files between my devices.
I guess this is not because of how good the “AI” is, but because it automatically gets note resources than any human player.