2000 Chevrolet Blazer • 170,000 miles

With engine running my battery warning light illuminates and the voltage indicator drops to 9 instead of normal 14 and will stay this way for sometimes a few seconds to sometimes a few minutes and will then slowly rise back to normal and battery light goes off. I suspect a bad alternator but need further assistance because its erratic or intermittent. Thank you.
May 2, 2013.

Symptoms indicates a failing alternator. The carbon brushes are worn resulting in intermittent contact.
When problem occurs, tap the alternator with a hammer and if the charging goes back to normal, that would confirm the alternator is bad.

May 2, 2013.