A Definitive Guide To Test Your Car Battery With A Digital Multimeter

A multimeter is an indispensable tool for any handyman. They can be used for many different purposes and are essential for troubleshooting electrical systems and components like car batteries.

A Definitive Guide To Test Your Car Battery With A Digital Multimeter
A Definitive Guide To Test Your Car Battery With A Digital Multimeter

While it’s fairly easy to check the voltage of your car’s battery, you’ll still need to be familiar with a multimeter in order to get reliable readings and make an accurate diagnosis. While hiring a contractor eliminates the possibility of an accident or mishap, the process is more complicated than doing it yourself.

The easiest way to determine the health of your car’s battery fast and precisely is to use the volt-ohm meter described in this article.

Testing a car battery using your digital multimeter

Testing the voltage

Some vehicles have a voltage readout in the dashboard, but as it measures the power coming from the alternator and not the battery, it is of little value in determining the battery’s condition. Learn how to check the strength of your battery packs here.

1. Set the multimeter

The red probe goes into the power jack and the black probe goes into the COM jack to start.

Digital multimeters can be either auto-ranging or manual-ranging, and the two modes are represented by separate dials. If you don’t already have one, you should get a multimeter that has auto-ranging functionality. To begin, the multimeter may automatically select the correct measuring range.

2. Battery polarity

The positive connection of the battery should be linked to the red probe, while the negative terminal should be connected to the black probe. The positive terminals of most car batteries are color-coded red for ease of use.

To a lesser extent than when measuring current or giving a jump start, polarity is not as much of a concern while measuring voltage. Simply reversing the polarity will result in a reading of -12.6v on the voltmeter, rather of the expected 12.6v. You can quickly return to work by switching the probes.

3. Provide a light load and check the readings

Start by turning on the headlights for 30 seconds with the engine running to eliminate any parasitic charges that could skew the data.

To make sense of the multimeter readings at 27 degrees Celsius, considering that the voltage of a car battery varies with temperature, consider the following:

  • A completely charged and healthy battery will have a voltage greater than 12.5 volts.
  • If the readings are between 12 and 12.3 volts, your battery is working at 75% of its capacity and you have some time before you need to replace it.
  • Finally, if the voltage of your battery is about 11.8 volts, it is only about a fourth of the way to its maximum capability and should be replaced immediately.

Keep in mind that the cold-cranking amps of the battery are irrelevant here; only the voltage matters. Don’t expect your car to start by turning the key if it’s below freezing outside; even a fully charged battery may not have enough electricity to run the starter. As such, it is necessary to do a load test on the batteries. Most individuals don’t own a load tester, therefore it may be necessary to take your car into a shop in order to get the battery checked out.

What to do in case of a low reading

You should use a smart battery charger on the battery right away if the voltage is below 12.60 volts. The battery’s voltage may have dropped over the course of several days if the car hasn’t been used. A quick charge can take care of that. Whether you charge it, you can retry the test to see if the outcomes have changed. A new car battery is needed if the current ones aren’t working properly.

Alternative: start the car and let it run at a steady idle for 10 minutes. It is also possible to test the alternator’s performance by measuring the battery voltage with the engine running. If your car’s battery isn’t getting fully charged, the problem can be the alternator.

Between 13 and 14.6 volts is the sweet spot for an idling vehicle’s battery voltage. When it falls below that mark, a new alternator is required. The battery will eventually be damaged by the alternator’s failure, therefore ignoring the issue will only make it worse. In the long run, switching it out will save you money.

Checking the terminals of your car battery using a digital multimeter

Your car’s battery might be fine, but the problem could be with the connections. It may be difficult, if not impossible, to start the car if the battery terminals are dirty, corroded, or loose.

While a loose battery terminal is obvious, other forms of faulty connections may be more difficult to see. A multimeter is useful in this circumstance as well.

You’re going to need assistance with this.

Here’s what you need to do:

  • The first thing you need to do is remove power to the engine’s starter or fuel injectors. Separating the ignition coils will disable the ignition system, while removing the fuel pump relay or fuel pump fuse will disable the fuel system. Look at the manual that came with your car’s service equipment for directions.
  • If the key is removed from the ignition, it will not work to start the car. When cranking the engine, shutting off the fuel supply is necessary to prevent it from flooding.
  • Finally, attach the black probe of the multimeter to the positive terminal of the cable and the red probe of the multimeter to the positive post of the battery.
  • The engine shouldn’t be started until someone has adjusted the multimeter to the 2V reading.
  • The reading on the multimeter should be below half a volt. You should check the condition of the outpost and the terminal and clean it up if necessary.
  • Reversing the process will allow you to focus on the opposite side.

Taking a leak test on the battery cover using a DMM

Deposits will accumulate on the case of your car battery if you don’t maintain it clean. Electrons may leak from the battery if dirt or acid is present on the posts.

A digital multimeter can instantly identify if a battery has leaked, whereas a visual inspection will reveal nothing.

  • The red probe should be inserted into the multimeter’s Voltage port, the black probe into the COM port, and the dial should be set to the lowest voltage measurement.
  • Turn on the multimeter, and then connect the black probe to the negative wire of the car battery while the red probe touches the cover.

There may be a leak of charge from the battery due to deposits if your multimeter reads any voltage at all. To remove filth from the battery cover and neutralize the acid, you can either use a professional car battery cleaning solution or some warm water and baking soda.

When one electrical component pulls power from another even when the engine is turned off, this is called a parasitic drain, and a parasitic drain test can help you find the culprits and prevent your battery from being constantly drained.

Final verdict

If you follow these steps to the letter, you should have no trouble figuring out what’s wrong with your car’s battery. Since a visual inspection alone is insufficient, a digital multimeter stands in as a proxy for having a professional auto mechanic check the charging system. Call your mechanic if you have any doubts about why your car might not start in the morning. By adhering to the recommendations of a trusted mechanic, you can save both time and money.

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