The voltage drop on the charge wire is proportional to the current flow. If there are no other loads on the charge wire, then the battery will charge quickly, at first. It will draw more current, so the voltage at the battery terminals might be substantially lower then at the alternator. As the battery charges, and the current flow falls, so do the losses on the charge wire. When current flow is zero, then the voltage at the alternator, and the RV battery is the same.
But all bets are off if you are running your fridge
, or some other power hungry appliance. Then the current flow on the charge wire will cause a voltage drop that, if the charge wire is not sufficiently large, may be so bad that the RV battery to drains to feed the fridge
. Leaving you with no lights
at the camp site.