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What voltage should the alternator put out at idle?
What voltage when reved up?

(2001 Lexus ES300)
in Metairie, LA on August 05, 2011
I'm getting 13.6 volts at idle but when I rev the engine the volts drop below 13 volts. The battery may be bad as it only reads 10 volts with engine off.
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Popular Answer
Have the battery tested both with a hydrometer and high rate discharge test to see if it is good (probably not. At rest voltage for a fully charged "good" battery is 12.6 volts an alternator that is charging will read 14.6 approx across the battery with the engine running. also take a reading at the large B+ alternator terminal and see if the voltage is higher there indicating bad connections.
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