14.2 is about right for a charging battery off a running motor/alternator, although having said that it should drop down as the battery is charged, it is normal for a 12v to show around 13-13.5v when charged.
(not 6 cell batteries as 6 cells in series will only ever give 12v just as 6 cells in parallel will only show 2v)
If your battery is indeed charging which it appears it is it is probably likely that she aint holding her charge for too long and as it is colder now it will definitely become more apparent if your battery is failing... good luck.