chassis may have come off the ford, or other mfg plant in 2011
but the RV was built on that chassis, in the latter half of 2012 to be a 2013 model
there is a difference between chassis year and Model year
the batteries were put in after the 'coach' was built
the coach/house batteries were installed in 2012, 4yrs old max
none of this really matters (except for future reference when looking for chassis/engine/transmission service) if the batteries need replacing, they need replacing
vehicle service ( not RV appliances ) goes by chassis year, shocks suspension engine chassis electrical etc.. its all listed/related to 'Chassis' year