i would put a meter on it just to have a little peace of mind. but like already mentioned its not uncommon to 'see' the difference between a ~12.75v battery and the ~14v while its charging.
also, make sure that one of your new batteries isnt FUBAR, if you have one battery in a bank with a bad cell it will drag down the other good battery, thus a larger voltage jump when the converter powers up
'14 XLR 395AMP
'16 Ram 3500 DRW, 6.7 cummins w/aisin trans and 4.10 gears