i think unless you have a truck with you.. the reading should be within the range of 13.5V-14V.... yung mga trucks ata kasi 24V ang output eh...

as for the alternator..we are reading the output of your batt and not the alternator... different alternators have different ratings.. 45AMPS, 55AMPS, 60, 70, 80, 110.. etc.. but those are amp readings.. they still put out about 13.8V (as regulated by the IC or regulator at the back of your alternator)...