How to Use a Multimeter to Test a Car Battery?

Sometimes, the car doesn’t start when you try and crank the engine. The most common area of fault here is the car battery. In the usual cases, you would try to jump the battery, and the car might start. If the car starts with the help of jumpers, you can be sure that the issue was with the car’s battery. Now, there can be multiple issues here. The first thing could be that you left the lights on, and it drained the battery. The second thing could be the issues with the car battery.

You might not want to visit a garage if it is just an issue with the car battery. You can order and replace the battery yourself, but how can you be sure about the issue? We will tell you how you can test your car battery using a simple multimeter. We will also tell you how to test the battery for dead cells and test the alternator. The only thing that you would need is a screwdriver and a multimeter.

If you do not have a multimeter yet, then you can order it before. These instruments are available very quickly. You will also be able to use them to troubleshoot many other electrical appliances at home. So, let us move ahead and share the details of how you can use a multimeter to test a car battery.

car battery

Special Instructions

It is crucial to ensure that the multimeter is set to the correct settings. While measuring the voltage, ensure that you set it on the voltage, and you should have that kind of tolerance set for the multimeter. Similarly, while measuring the amperage, make the settings accordingly. Setting a lower range may destroy the multimeter, and the brand will not cover it in the warranty. So, ensure that you are setting up the multimeter right before you use it to test the car battery.

Optimal Battery Capacity

Knowing the optimal values would help you in testing the battery and arriving at a conclusion. Now, we do not recommend you to check the battery right after the trip. Instead, you should leave the car overnight and then check the battery. This reading would often be referred to as resting voltage, and it should be in the range of 12.5 volts. The resting voltage will help you in understanding the health of the battery.

You can also check the amperage of the terminals, and you should get 14A to ensure that the car is charging the battery correctly. Now, let us move ahead and check out the various ways to test the car battery using a multimeter.

Checking the Battery with Multimeter

To check the car battery with a multimeter, you need to first prepare the battery. If you are not sure about what you need to do, do not worry and follow the steps listed below.

  • Start by opening the hood of the car. You will be able to find the battery in the engine bay. It would be covered with a panel, and you will have to unscrew or unclip the hinges to remove the panel. You will notice the battery connected by two wires, and one of them would be red while the other one would be black.
  • Remove the covers from the terminals and scratch them using a screwdriver. Scratching them is important because there can be oxidation of the terminal, making contact difficult.
  • Adjust your multimeter to 20V DC and check the voltage by touching the red probe to the positive (red) and black probe to the negative (black) terminal. You should get a reading over 12.5 V. If you are getting a reading of 12.2 Volt, then that means that the battery charge is just 50%, whereas, at 12V, there is no charge in the battery.
  • If you want to be sure about the battery health, charge the battery to 100%, disconnect the battery and leave it overnight before you take a reading. This will ensure that you are not getting inaccurate readings because of parasitic loss.

Checking the Alternator with Multimeter

There can also be a possibility that the battery is alright, but there is an issue with the charging mechanism. The alternator is responsible for charging the battery. If it is not working as designed, then the battery would not charge. Below are the steps on how to check the alternator with a multimeter.

  • Park the car in Neutral and turn on the ignition. Set the multimeter to 20 V and touch the probes like listed in the previous section.
  • This will return you a value of close to 13.5 V to 14.5. If you are not getting the voltage between the given range, then there are chances that your alternator needs to be checked.
  • This can be an expensive procedure, and you will need to get the alternator checked. Not getting the proper voltage from an alternator can also damage your battery.

Checking the Battery for Dead Cells

Well, the dead battery cells cant be checked using the multimeter. To test the battery for the dead cells, you need to first ensure that you have access to individual cells. If you do, then you would need the hydrometer-style battery tester. You would need to review each cell and asses the readings. We would recommend you to avoid this test and instead check with a professional for a solution.

Final Verdict

It is easy to check the battery using a multimeter. You should give it a try before you visit the mechanic. This will help you in reducing the expense if you have to replace the battery of the car.

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