Thanks for the advice. I think it's new converter time. I got the 4 volt DC reading with the battery disconnected and also at each 12V DC circuit on the panel, so it appears that I am indeed getting only 4V output. The converter is a Parallax 7155, and I see that direct replacements are available. It also appears that the 7155 is not a "smart" charger, so maybe I'll look for a better replacement. I will double check to see that I am getting 120V to the converter (not just to the main panel) in case there is a problem with the breaker.
Bill