Charging system

Here are some steps to take to check the charging system. You will need the following items

a battery load tester, a volt meter, or some type of charging analyzer tester.
1)To test the condition of the battery you need a load tester. This will put a load on the battery and tell the condtion of the battery. Most people don't realize that the battery is part of the charging system and the # 1 cause for breakdowns
2) Test the voltage output of the alternator by connecting a volt meter to the battery. (Neg of the bateery to the neg of the meter and pos to the pos) The average car should put out between 13.2 to 15.2 volts. As more accessaries ar turned on the votage will drop, but should not go below 13.2
3)Also don't forget to check that the battery cables are clean and tight. In addition check the alternator belt to see that it is properly adjusted and not slipping. Hope this answered your question :D Backyardmechanic

To test the alternator output car must be running