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"   A resistance-type battery tester can tell if your car battery is up to snuff. Q: My minivan has failed to start a couple of times recently, because of a low battery. It turns over, but won&amp;#039;t spin fast enough to catch. My mechanic says he tested the battery and it&amp;#039;s bad. But it&amp;#039;s only a year old. I checked the voltage at idle, and it&amp;#039;s 13.8 volts. All of the cells have plenty of water. I think it&amp;#039;s something else. A: There&amp;#039;s more to checking a battery than testing the voltage and looking inside for low water. For one thing, you need to check the voltage when the engine is off, not when the alternator is raising system voltage to its normal level. You can test for proper cranking voltage with a voltmeter while\u2014you guessed it\u2014cranking the engine. The several hundred amperes of current the starter motor draws should pull the battery voltage down to a normal 9 to 10 volts. Do this test: Disable the ignition or injection to prevent the engine from starting. Then put a voltmeter across the battery posts while cranking it with the key or an external remote starter button. Crank for 15 seconds (no longer); the battery voltage should remain 9.6 volts or above. (These are GM specs for a battery at 70 F; your mileage may vary.) Another way to check is with a dedicated battery tester that has its own internal resistor pack and voltmeter. This is a lot easier to use--you don&amp;#039;t need to disable the engine to crank it. Just check the voltage after 15 seconds. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/how-to/a2074/4221215/>