Vehicle Battery & Alternator Diagnostics

What does a multimeter reading of 0.5V AC across an automotive battery with the engine running indicate?

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 Correct IncorrectAlternators generate AC that is rectified into DC by a diode bridge. Excessive AC ripple voltage indicates a faulty rectifier diode leaking ripple voltage into the vehicle system.

What does a multimeter reading of 0.5V AC across an automotive battery with the engine running indicate?

• The battery is brand new and healthy
• The spark plugs are firing backwards
• A blown alternator rectifier diode leaking AC ripple voltage into the vehicle system
• The headlights are turned on high-beam