I have owned 3 RV's that came with WFCO converters. Two of them got PD units dropped in within a month, the other TT got sold after one trip because the wife didn't like it. We actually made money on that one because we bought it used at a good price and sold just before Memorial Day at a better price. I never saw any of the three WFCO units get above 13.4 even on a low battery. I carried my garage battery charger around until I got the PD's installed.
I also added a heavier charging wire to every RV.