Thanks! I checked all of the connections (5 of them...) this morning, and they all were tight!
I fired things back up: the Zantrex was reading 12.4 volts.
I fired up the generator again... it rose to 13.4
I shut things back down, and no beeping or error messages.
Did I somehow fix it??
In the meantime: I also plugged it in, for a good drink of some AC power!