Curious.....under charge the digital meter reads 100%.... 13.6V. At rest, fully charged....84%.....12.13V And the trailer "gauge" shows 100% What do you think?
Either your converter is not charging the battery properly, or your battery is failing and not holding a full charge, or the voltmeter installed in your RV is not accurate.
When charging a depleted battery, your voltage at the battery should be at least 13.6v. After charging for several days, turn the converter off and wait several hours to check the charge at the battery with a voltmeter. It should be at least 12.6v if your battery and charger are working properly.