alternator??? on 2002 Volkswagen Golf TDI

my car starts just fine, but when i test out the volts level on the battery it says 12.31. what does this mean. do i need a new alternator? or is it something else?

Asked by for the 2002 Volkswagen Golf TDI
Sounds like the Alternator is suspect. Also check the wiring and make sure that the batter is still good, i.e. less than 4 yeas old.