Battery light

It was autozone...just used the voltmeter they have and a code readout thing that said the charging system was ok...I couldn't tell you more beyond that. I'm just trying to determine if it is in fact the alternator, before I take it into a dealership and pay a diagnostic fee... I can replace the alternator, not so sure about anything else electrical...PCM or voltage regulator something more involved like that. What do you think?

voltage regulator is built in the alternator.have you checked all the connections,battery,alternator,grounds free of corrosion,clean,tight,all connected?do you have a volt meter?if so,put it on dc volts.check the battery voltage with the car off,should be 12.6 volts.then start it up,do the same test on the battery with it running,should be 13.5-14.5 volts.