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How Do I Test My Car Battery?

American Government Special Collections Reference Desk

How Do I Test My Car Battery?

Elliott Turner
2 September 2008


There are many variables and circumstances that can alter the results of your battery test, so it is important to take all these variables very seriously before actually making an attempt to get an accurate reading of the value of your battery.

To test the battery in your car, first you want to remove the surface charge. If you don�t remove the surface charge, it can make a bad battery look good or a good battery look like it is bad. To remove the surface charge you can turn your headlights on for 15 seconds or you can allow the battery to sit for four to twelve hours in a warm room, around 77� F.

Once the surface charge has been removed you want to find out the battery�s state of charge with a hydrometer. The specific gravity should be 12.65. Then you might need to perform a load test on your battery to determine its condition. You will need to use a load tester for this test. The load tester may or may be accurate. If it is off by 20% - 50% that is a very significant amount and can make a big difference in knowing whether the battery is good or bad.

If the battery�s state of charge is a 75% or higher, then you can load test the car battery. With a battery load tester, you want to apply a load equal to one half of the cold cranking amps rating of the battery for 15 seconds, and then apply one half the vehicle�s cold cranking amps specification for 15 seconds. Disable the ignition and turn the engine over for 15 seconds with the starter motor. During this test the voltage should not drop below 9.6.

If the battery has passed the load test, then you should recharge the battery as soon as possible to prevent sulfation. This will restore the battery to its optimum condition. A better alternative than purchasing 3 different testers, which may or may not be accurate, is to purchase one accurate tester. There are plenty of testers on the market. Each one claiming to be the most accurate tester and it is hard to decipher which one to choose that will work for you or even work at all. Your best bet is to choose a proven method and while your choice may not be as inexpensive as you would have wanted, you will find that you get what you pay for.

Do you know the recommended battery tester for your application? Get all the details and find out more at http://batteryresearchcenter.com/battery_tester/

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