Two friends have said two seperate possible reasons why…1) the alternator may be dead–need a new one, and 2) the computer system has a glitch in it. When jumped, the car starts (barely), and after running for a while (an hour at least), it still does not maintain enough power to start again thereafter. New battery or new alternator? Know of a way to check these things out myself?
If you have a voltmeter, try these basic tests:
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Test the battery voltage twice. First, connect the voltmeter leads to the connectors (not the battery posts). Next, connect directly to the posts. You should see about 12.4 volts, both times. If the readings are different, your cable clamps are loose. Do this with the engine off.
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Repeat the above test, with the engine running. You should 14 volts or so. If you read 14 volts on the clamps, then your alternator is putting out. If you read 14 volts on the battery posts, then your battery clearly isn’t holding a charge - replace it.
If you don’t get 14+ volts at the clamps, check every connector in the path. Make sure the ground cable is tight at both ends, and trace the hot cable back to the alternator, checking every junction along the way.
Any corroded or loose connection can keep a perfectly good alternator from charging a perfectly good battery. Cables can also go bad, but bad connections are more likely - I’ve had this happen to me with several different cars.