Smart charging systems which are increasingly common on vehicles are designed to reduce emissions and increase fuel mileage. One effect of this is that they don't fully charge the battery. ie 12.4V may be considered completely adequate for starting the next time for example. Different battery types are being used to provide good performance and service life with the partial charge for starting.
And they are definitely not designed to charge auxiliary batteries. So don't expect that your camper battery will be fully charged or even hardly charged when you stop for the day.
One owner solution is to install a DC to DC charger that boosts the voltage and applies the correct multi stage charging algorithms based on the auxiliary battery type independent of the main battery type and charging.
