Hi Don,
I had a look on the manufacturers web site but your charger doesn't seem to be listed. They make three distinct types - a normal three stage charger, a non-charger that is more like a fixed power supply providing 13.7 volts, and another type that switches between two voltages.
You said in your last post -
"My first choice was to up the habitation
battery to 110 Ah.
Battery was checked by meter and tested on a 50-Watt output to establish duration.
Battery appeared to be in good shape.
Exchanged 85 Ah for the 110 Ah. And this appears to be the start of the problem. The
battery was fully charged when put in, linked up to the van, checked again with meter and holding charge."
so putting a different "good" battery in the system was the start of the problem.
No reason to think the charger would pack it in at that instant (although the difference between the traffic light indicators and the measured voltage needs explaining, but this could be just the way the unit derives the indication), so I would still be inclined to initially suspect the "new"
battery or something to do with the installation of the
battery even if it was brand new. The fact that the voltage rises to 16.5V is interesting - depending on how long it takes for the voltage to reach that point -- in that if the
battery was good and the charger was current limited, I would expect a reasonable delay (many minutes) for the volts to get that high. A high resistance cell could cause that to happen quickly if the three-stage charger was trying to pump the rated bulk charge current into the
battery.
Diagnosis using some of the visual and electrical tests I suggested above might narrow it down. Other than that, taking it to a
battery place for a proper load check may be the best solution.
Voltages need to be measured right at the
battery lug itself to avoid possibility of a bad connection. I assume that is where the multimeter reading was taken.