Car won't start with own battery, runs fine once boosted.

1991 BUICK PARK AVENUE
180,000 MILES • 2WD • AUTOMATIC
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KAISO
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1991
Buick Park Avenue
Engine size: Do not know
~180k km

The battery doesn't (appear to) hold a charge large enough to start the car after it's been turned off. Starts fine with a boost. Two batteries tested with same result. Car has driven 30+ minutes with lights/radio on with same result after it is turned off.
Jul 5, 2011 at 4:00 AM
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RASMATAZ
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Have the alternator load tested if okay check and test the starter motor
Jul 5, 2011 at 4:22 AM
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MHPAUTOS
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Road test battery after a full bench charge, this will show up a faulty battery or not.
Jul 5, 2011 at 4:44 AM
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RASMATAZ
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Get a voltmeter and read the battery voltage before you start it- and while engine is idling. if you have 13.5 -15.5 volts the alty is doing its job-comeback with the readings
Jul 5, 2011 at 4:47 AM
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DANLESABRE
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Are the battery terminals tight? Can you wiggle them by hand?
Jul 5, 2011 at 4:48 AM
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