How many volts should be at the starter

Q: Recently, my minivan failed to start a few times because the battery is weak. It was rolling, but not fast enough to catch it. My mechanic said he checked the battery and it was bad. But it's only a year old. I checked the voltage at idle and it is 13.8 volts. There is a lot of water in all the cells. It looks to me like something else is going on.

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A: Testing a battery is more than just checking the voltage and seeing if there is a small amount of water in it. First, you should check the voltage with the engine off, not when the alternator is bringing the system voltage to normal values. You can use a voltmeter to check that the starting voltage is correct when you start the engine. The few hundred amps drawn by the starter motor should bring the battery voltage down to a normal 9 or 10 volts. To perform this test: turn off the ignition or fuel injection so that the engine will not start. Then place the voltmeter on the battery terminals while starting with the key or external remote start button. Run for 15 seconds (no longer); the battery voltage should remain at 9.6 volts or higher. (These are GM's specifications for a 70°F battery; your experience may vary).

Another way to check is to use a special battery tester that has its own internal resistor and voltmeter. It's easier to use: you don't have to turn off the engine to start it. just check the voltage after 15 seconds.

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