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Car Battery Leak Test

Updated on January 21, 2016
A car battery leak can discharged your battery overnight.
A car battery leak can discharged your battery overnight. | Source

Car battery leaks are not normal. And any abnormal electrical draw on your car battery can potentially discharge it and leave you stranded. However, unlike parasitic loads (current draws through electrical devices that continue to pull current after you shut off the engine) current leaks come through an acidic layer that accumulates over time around the battery case, usually due to poor or no battery maintenance.

The average car owner can easily diagnose the leakage and fix it, though. In fact, you can complete this simple task in about an hour. You'll need some simple tools, cleaning supplies, and, although you don't need to know much about electricity, a digital or analog voltmeter.

NOTE: If you want to test for a parasitic drain or this current leakage test comes up negative, read the article Car Battery Problems: Parasitic Battery Drain Tests to check for a possible power drain from a load. You can do this test at home using a digital multimeter, too. Also, take into account the age of your battery. Usually, car batteries have a useful life of four to five years. If your battery holds power for short periods at a time, and your tests don't point to any other problems — including the charging system — your battery may have reached the end of its service life. This article on using a hydrometer will help you find out the state of health of your battery.

Tools you'll need:
Digital or analog voltmeter
Baking soda
Warm water
Small bowl
Soft brush
Paper towels
Battery post cleaning tools, if necessary
Distilled water, if necessary

How to Do a Battery Leakage Test

This simple test will help you detect any electrical current escaping across the top of your car battery case.

Usually, a visible layer of dirt or any type of foreign residue on top of the battery or around the case could lead to a power leak. Even if your battery case seems clean, but you've experienced low battery charge or battery discharge problems for no apparent reason, continue with this test anyway so that you can discard a power leak as you main problem.

1. Plug in the black meter probe into the jack marked COM, and the red meter probe into the jack marked with DCV.

2. Set your digital voltmeter to a low range on the direct current (DC) voltage scale and turn the meter on.

3. Touch the negative battery post with the negative probe of your voltmeter. The negative battery terminal has a minus sign (-) next to it. Your voltmeter negative probe has black insulation.

4. Now, touch the positive (red) voltmeter probe at different points across the top of the battery without disconnecting the negative probe from the negative battery post. If your meter detects even a small amount of voltage during your power leak test, you've found a power leak and need to clean the battery case.

Proper car battery maintenance can prevent power leakage.
Proper car battery maintenance can prevent power leakage. | Source


Keep your battery away from appliances with open flames like dryers and water heater to prevent an explosion.

Car Multimeters

Actron CP7677 Automotive TroubleShooter - Digital Multimeter and Engine Analyzer
Actron CP7677 Automotive TroubleShooter - Digital Multimeter and Engine Analyzer

* Includes protective boot, detachable color-coded test leads and alligator clips

* Automatic zero adjustment for volts and amps for accurate measurements

* Automatic reverse polarity indication

* Overload protection on all ranges and fold-out stand for better viewing

* 1-year warranty


How to Clean Your Battery Case

To thoroughly clean your battery, it's a good idea to remove it from your car and set it on a workbench or similar work area.

NOTE: Protect your eyes during this procedure. Whenever you need to handle a car battery, it's a good idea to wear goggles and chemical resistant gloves. The sulfuric acid inside your car battery can leave you blind if your eyes come in contact with it. Even the small amount of acid buildup that may accumulate on your battery top may cause permanent damage.

1. Use a wrench and a pair of pliers to disconnect your battery from the tray and cables.

2. Disconnect the hold down mechanism to free the battery. Also, check that the mechanism is in working order. If your battery shakes as your car moves down the road, it will reduce its service life. If this has already caused damage, it may explain your battery failure to hold the charge.

3. To service your battery, use a space in your garage or work area away from appliances with open flames like dryers and water heaters. The chemical reaction inside the battery produces hydrogen gas that can suddenly ignite. And if the gas ignites, your battery can explode. So don't take a chance.

Wear goggles when working on your car battery to keep sulfuric acid away from your eyes.

4. Prepare a solution of 1 tbsp. of baking soda per 8 ounces of warm water in a small bowl.

5. Thoroughly clean the battery case and posts with the solution using a soft brush and wipe the case with paper towels. Don't let the solution seep through the battery vent caps, if you have a non-free maintenance type battery. The solution will ruin the electrolyte and your battery.

6. As you clean the battery case, check it for physical damage like cracks, loose battery posts, and bulging spots. Any of these problems may lead to battery charge drain. Replace the battery if you find any signs of physical damage.

7. Then, check the terminals on your battery cables. Do they seem oxidized or corroded? Clean them as well using the solution and a battery post cleaning tool.

8. Clean the battery tray as well with the solution, the soft brush and the paper towels.

Checking Battery Electrolyte

Many car batteries now come as free maintenance, which don't require a periodic electrolyte level check. However, if you have a battery with removable vent caps, you need to check the acid level after thoroughly cleaning the battery case.

* With your battery still on the workbench, carefully remove the vent caps from the top of the battery using a standard screwdriver.

* Using a flashlight, if necessary, look through the filler cap openings and check that the electrolyte covers the battery plates and their separators. For better reference, if the filler cap openings have a filler ring indicator, the electrolyte level should reach the bottom of the filler ring. Otherwise, add some distilled water through the filler opening using a small funnel. Don't use tap water to refill your battery; the chemicals and impurities in tap water will settle at the bottom of the battery and can short out the plates, ruining your battery.

* Once you've replaced the vent caps, repeat the leak battery test using your voltmeter to confirm electrical current has stopped drawing off the top of your battery case.

* Install the battery on its tray and secure it with the necessary hardware.

Even a car bat-tery needs proper care.
Even a car bat-tery needs proper care. | Source

Now that you know how to test a car battery for current leakage, check it regularly and remove dirt and corrosion buildup as necessary, even if you don't detect current draw. Poor maintenance can drastically reduce your battery efficiency. This simple procedure will help extend the service life of your battery, says James E. Duffy in Modern Automotive Technology. Plus, it will help you avoid some issues associated with common dead battery problems.


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