The alternator should be putting out in the neighborhodd of 13.7 to 14.2 volts if all is well (maybe a bit higher if cold it is or lower if hot); so your gauge seems accurate. You may be thinking of the battery voltage with the car not running and nothing on; well charged and with any charge removed for an hour or so, the battery sill read 12.6 to 12.7 volts if in good shape.