The voltage regulator inside the alternator is bad.
Volts
If the alternator is only putting out 12 volts then it is defective and needs replacing. It should output from 13.5 to 15.5 volts DC. You will need a digital volt meter to get an accurate reading. Analog volt meter is not accurate enough.
A device that measures volts.
A volt meter or a multimeter on the voltage scale.
12.6 volts as read with a digital DC volt meter.
It is a 12 volt battery. Fully charged it will read 12.6 volts with a digital volt meter.
A fully charged 12 volt battery will output 12.6 volts are read with a digital volt meter.
14 volts
If this is a consumption meter with 120/240 volts, the answer is yes.
All voltage reading are usually read with a volt meter. This volt meter can be a hand held unit like electricians use.
With a voltmeter Keep volt meter terminal on phase and neutral wire and it will show the exact volatage
Fully charged it should read 12.6 volts with a digital volt meter. 12.4 = 75% charge, 12.2 = 50%, 12.0 = 25%.