Voltage gauge on dash registers lower than it should on a 2000 mercury grand marquis; is this a common issue

Should be around 14.5 it's still charging but not where it should be probably bad voltage regulator which is inside alternator have to change alternator to change regulator they run a little over $100.00 but before you change alternator check voltage right at the battery if you have 14.5 at battery your okay there is something wrong with the dash gauge,

I got 2000 gran Mara bat good put two new alts on it bat lite stay on constant went Auto salvo got one off 2001 Mara now bat lite off now shows low volts but does not move wen I turn everything on very odd