How to Test a Car Battery with a Multimeter

Want to test your car battery but not sure how to do it? This guide shows you how with a multimeter. So you’re not sure if your car battery is working? Well there are few things more frustrating than your battery dying in the middle of a road trip. Fortunately with a multimeter you’ll be able to check its status and if it needs repair.

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Your car battery is necessary to propel the starter motor and get the engine revved up. If you plan on going somewhere, consider sparing a few minutes to check your car battery. With a multimeter you’ll be able to do this quickly and accurately.

Step 1. Find the car battery

Lift the hood and look under the engine compartment. Most car batteries are stored there, but in some cars the battery is in the trunk. Check your car manual for information.

Step 2. Check the battery terminals

Once you find the battery, inspect the cables and terminals for signs of damage or corrosion. One sure sign of corrosion is a yellow green crust. You have to get rid of this first as it might affect the multimeter readings.

Step 3. Remove corrosion

If there is corrosion, use a terminal brush and battery terminal cleaner to remove it. Clean thoroughly before proceeding.

Step 4. Secure the cables

Check for any loose cables. Tighten any loose ones you see. Use a 5/16 inch nut or a Philips screwdriver to tighten the cables. Refer to your car owner’s manual for any specific tightening tools recommended.

Step 5. Ready the multimeter

Insert the test leads in the proper multimeter jacks. Insert the black lead in the COM connector. The red test lead goes into the connector with the label amps, ohms and volts. Do not use the 10A jack / connector if your multimeter comes with one.

Step 6. Set the multimeter to volts direct current

When the test leads are in place, adjust the multimeter dial so it is at 20 VDC. An alternative is to find the nearest current option above 14 V. If you cannot find the direct current, look for a dotted line with a solid line above it. That is the symbol for DC.

Do not choose an AC or alternating current. The symbol for the AC on multimeters is a squiggly line with a number over it.

Step 7. Read the multimeter

Look at the multimeter display. It will say 0.00.

Step 8.  Test your car battery

Now that your multimeter is ready, it is time to test your car battery.

• If you haven’t done so already, turn your car’s engine off. Testing with your car running will affect the reading as the alternator interferes with the multimeter.
• Put the red lead on the battery terminal marked red or positive.
• Put the black lead on the battery terminal marked black or negative.
• Check your multimeter reading.
  • If the display states 12.4 VDC, it means the battery is charged fully.
  • If the display reads 12.2. VDC, the battery is charged at 50%.
  • Any reading under 12 VDC indicates the battery is dead.
  • A normal car battery usually has a 12.6 VDC as it is the sum of half a dozen 2.1 volt internal cells.

Step 9.  Start your car’s engine

Ask someone to start the car’s engine while you keep an eye on the multimeter. The V reading should not go under 10.0 as long as the key remains in the starting position.

If the multimeter states anything below 10.0 VDC, it means your car battery is unable to generate sufficient current to cope with the motor’s present draw.

Step 10. Turn the car engine off

If you turned the car on, turn the engine off now. Find the battery cable terminal end and put the multimeter test lead there.

Read the multimeter display. It should be around 0.1 volt of the highest reading listed in step 8.

How to Use a Multimeter to Check for a Battery Leak

A leak is one of the leading causes of batteries suddenly suffering damage. Sometimes visual inspection is not sufficient and you’ll need a multimeter to help you out.

As acid and dirt accumulates across and over the terminal, the charge starts to leak. You can use a multimeter to check if there is a leak on your car battery.

• Turn your multimeter on.
• Activate your multimeter and set it to voltage.
• Let the meter black probe make contact with the battery negative terminal.
• Let the red probe make contact with the battery cover.
• If there is even the lightest voltage registered, there is a leak.

How to Check the Status of Your battery terminals

Loose, corroded and otherwise dirty battery makes it difficult for a car to start, if not impossible. This is also one of the most common reasons why batteries suddenly go dead. However this is a problem that is easy to spot if you have a voltmeter or better yet, a multimeter.

In the following steps you will take a look at the battery terminals and check for signs of voltage drops.

Step 1. Turn the ignition system off

There are two ways to do this. The first is to remove or relay the fuel pump fuse.  The second is to disconnect the ignition coil. Either of the two methods will prevent the engine from running.

Step 2. Connect the probes with the battery terminals

Similar to the steps earlier, touch the red probe of your multimeter to the positive battery post. Touch the black probe onto the battery post’s cable terminal.

Step 3. Start the engine

Turn the engine on and read the multimeter display. If the meter reads 0.5 V it means the battery terminals and post need to be checked and possibly cleaned.

Step 4. Check the other battery terminal

Get your multimeter black probe and make contact with the battery post’s negative part. Now get the red probe and let that make contact with the cable terminal linked to the same battery post. This is the same as in the previous step, only the probes have been reversed.

Step 5. Turn the car engine on

Turn the car engine on and read the multimeter display. If it reads 0.5 volts, clean the battery and look for signs of damage.

How to Keep a car battery in good shape

A multimeter is a handy tool in determining if there is something wrong with your car battery. However you can also d your part by performing regular maintenance on your car battery.  This should only take 10 minutes.

Things You’ll Need

• Set of wrenches
• Cable puller
• Hydrometer
• Multimeter side terminal or post cleaner

These are all available in auto part shops.

Step 1. Clean up the cable corrosion

Start from the top of the battery and go around to the cables. Use a post cleaner for this. You can use a car battery corrosion cleaning kit or mix a nonmetallic finish, a cup of water and a tablespoon of baking soda. Flush it down with water, preferably cool.

Loose the clamp bolts on the cable and twist it a little. If it won’t come off, use a cable puller. Or if you got a side post terminal, a 5/16” wrench will do. Use a post cleaner to remove any more corrosion you see.

Step 2. Assess the electrolyte level

If the battery requires water, make sure to use only distilled, clean water. Don’t allow the cells to spill over.

Carefully remove battery cell covers. You’ll see the mixture and water is about half an inch deep. Again, make sure the water does not overflow if you add more.

Replace the battery if there is a crack as that cannot and should be repaired. Allow the water and electrolyte mixture to settle for a few hours.

Step 3. Check the battery condition and charge

Test the electrolyte cell by squeezing the hydrometer ball, pulling the solution close to the tester. Grab the test level, take note of the reading and send the solution back in each cell.

When testing cell electrolytes, make sure you hold the tester level carefully and take note of the reading. Make certain the solution is squirted in the same cell. Testers have been calibrated with the assumption the battery is 80 F.

Add .04 for each reading per 10 degrees that it is above 80 F. Deduct .04 for every 10 degrees below 80 F. If the cell reading deviates by .05 or greater, you need a new car battery.

A fully charged battery should read 1.265 at least. Any reading of 1.200 or lower means the battery should be replaced.

Do these on a regular basis and you will never be caught unaware if there is a problem with your car battery.

Car Battery Electrical Faults

A lot of cars today have alarms or computers that can detect if there is an electrical problem with the car battery. If your car does not have one and you are concerned about a power drain, buy a DC amp meter. These are easy to use as you just need to put the sensor clips On the battery cable and check the results.

Additional Car Battery Maintenance Tips

Check the water level of the battery every 2 or 3 months, but only if it is a wet cell battery that’s not maintenance free. If you have an AGM battery, they rarely if ever need water and should not be opened. You can check the mixture level by pulling up the fill caps.

Clean the battery terminals every 6 to 8 months with a wire brush. To clean:

• Take the connectors off. Move the connectors side to side and give it a soft pull.
• Dip the wire brush in a paste made up of water and baking soda.
• Brush the terminal until the acid buildup has disappeared.

Conclusion

Inspecting your car battery is not as complicated as some think. All you need is the right tool and you’ll figure out if the battery is ready or not. The time you spend in inspecting your car battery with a multimeter can make the difference between a frustrating and enjoyable ride.