Hi,
What brand/make and model and size is the power converter? And how old is it?
Do you have a voltmeter? When the converter appears to get to 75%, what was the charging voltage before the 75% and then after the 75%? Do the test at the battery terminals and ideally reported in at least one decimal point, 2 decimal points is better.
Also, how long was the system sitting at 75% and not going any higher? A few hours or a day or more not gaining any higher state of charge.
What are you using to measure state of charge?
We are making the assumption your system worked before and now does not. Is that the case, or did you just buy the camper and this is what you have?
By chance, was there any power draw going on inside the camper when the system stopped charging any higher? If yes, what was powered up?
What group size twin battery's are they? Group, 24, 27 31 etc. And are they lead acid or other technology.
We need some more background to help back into what might be the issue to give better answers.
Hope this helps
John
