How To Test A Car Battery With A Digital Multimeter?

testing a car battery with your multimeterAn automotive battery is an essential part of a vehicle. It is a rechargeable battery that supplies electrical current into an automobile.

It provides power to the starter to start the engine. Auto batteries are designed to release a high burst of current and then quickly recharged.

However, they are not intended for deep discharged. Full discharge can reduce their lives. These batteries are extensively used for around 1920.

The first charging and starting systems were designed to be 6-volt and positive-ground systems. And the vehicle’s chassis was connected to the positive terminal.

Now, all cars have a negative ground system which is where the car’s chassis is connected. As batteries play a vital role in a vehicle, it is important to know if they have enough charge.

So, here’s some idea on how to test a car battery with a multimeter. This would help you to know if the battery has enough charge.

What is Multimeter?

multimeter to test auto batteriesA multi-meter is commonly called as a VOM (volt-ohm-milliammeter) or simply, multi-tester. It is an instrument for electronic measuring with various measurement functions.

It can measure current, voltage, and resistance. There are two types of multi-meter which are analog and digital.

Analog multimeter, uses a micrometer with a moving pointer while the Digital displays and shows graphical bar to represent the measured value.

Digital multi-testers are more common because of their cost and precision. These can be bought at your local auto parts store or even online.

Testing a Battery Using a Multimeter

Loose, dirty, and corroded battery terminals can lead to dead batteries. Sometimes these problems are hard to spot with visual inspections only.

Battery check and regular checking of an electrical system are essential not only when the battery is showing signs of weakness. Lessening these problems is critical.

One of the most important thing to check in an auto’s battery is the charge. Use a multimeter to figure out how much battery charge there are in your car’s battery.

Testing a battery is an easy process. Follow these steps we provided below:

Materials needed:

• Safety glasses

• Protective gloves

• Multimeter

1. First, deactivate the ignition system to prevent the engine from starting. Do this by temporarily removing the fuel pump pulse or by disconnecting the ignition coil.

2. Fixed your voltmeter to 20 DC volts.

3. Touch the negative (black) battery terminal using the negative (black) meter probe while positive (red) battery terminal using positive (red) meter probe.

4. Look for an assistant and ask to switch on the headlights to give the battery with a light load.

5. Then check the reading of the voltmeter at a temperature of 80°F or 26.6°C. If the battery reading is 12.5 volts or higher, then it has much charge.

If it shows 12.4 volts, then it is 50% charged. And if it shows, 11.8 volts or lower, it has 25% or less charge.

Slow charge it to improve the chemical reaction of the battery then do the test again if it has a low reading.

Here are some guidelines.

12.66+ volts 100% charged

12.45 volts 75% charged

12.2 volts 50% charged

12.06 volts 25% charged

11.89 volts 0% charged

If the battery shows a reading of 0 volts, there are chances of battery short circuit. The battery has a dead cell if it cannot reach larger than 10.5 volts when being charged.

And if the charger says full charge but the battery has a voltage of 12.4 or less, then the battery is sulfated. Sulfation is a natural after-effect of a discharged battery.

Normally, charging the battery again will replace the sulfation crystals and change it back into the electrolyte to be able to create power again.

However, if the battery is left uncharged, critically discharged, or drained for some time, the sulfation will rise and solidify onto plates.

And this will cover the plates’ surface area which removes the chemicals required to provide power. It decreases the potential to reach a full charge, and it self-discharges the battery quicker than normal.

Diagnostic Test

If the battery is fully-charged, you can test it with a few methods.

• Load Test – To know if the battery is bad or not, you can make a load test. You can do this by starting the engine and monitoring the voltage using a multi-tester that has a min/max mode.

Hold the prongs of the voltmeter to the right terminal of the battery. During the load test, the car battery must provide at least 9.5 volts throughout engine cranking.

The battery must be fully charged to perform this test correctly. To do a load test follow these steps below:

1. Attach the multimeter probes to the battery.

2. Then, fix the voltmeter reading to 20 volts or auto-detect.

3. Mark battery voltage when the engine is off.

4. Crank up your car and watch the voltage fall on the multimeter.

5. If the voltage decreases less than two volts during cranking, then the battery is good.

6. However, if the voltage decreases more than two volts or goes under 9.5 volts, then it requires being substituted soon.

• Electronic test – It checks the battery cells via frequency test. Electronic test it the easiest way to check your auto battery without a multitester.

In this method, the electronic tester will send an alternating frequency signal by the battery to settle the status of the cells. Otherwise speaking, it measures the transit of the battery cell.

Checking Battery Leak

Normal batteries do not leak. To spot a leak from your battery, inspect for cracks in the casing of a battery and look for apparent proof of fluid dripping.

Look also for bubbling liquid seeping within the cell caps. Also, if you see that the battery is inflated or appear to be distorted, this means that the battery is broken and needed replacement.

Leak Test on a Battery Using a Multimeter

Car batteries are highly toxic and corrosive because they contain a sulfuric acid solution. For safety reasons, it is essential to handle leaking batteries with complete care and attention.

Use shielding eyewear and gloves. Always secure a leaking battery safely and securely, beneath from children and pets.

In this article, we talked about the importance of regular battery checking and how to test a car battery with a multimeter. Taking care of your automobile battery is only a part of taking care of your automobile.