. Old Converter , less than 13 volts.
I would also comment a bad reading I got from a Sunline resale.. Over time the original converters stat to make loud noise. I thought the lady seller gave me a very old Battery, but it turned out to be only one year old..... Voltmeter on the charger terminals showed only NINE Volts, as a circuit board in the unit was partially bad.... New convertors can be bought , Camping world , Amazon etc....
My quick fix was to unhook the wire & charge with my typical Sears garage charger & squeeze clamps. . Needle meter on the front garage charger..