How to Test a Car Battery with a Multimeter

When was the last time you thought about your car’s battery?

If you’re like most people, as long as the car starts and runs normally, there is nothing to worry about. That’s true most of the time but batteries don’t last forever.

To avoid being caught with a dead battery, you should consider performing a car battery voltage test periodically. This is probably the simplest and easiest way to check on the status of your battery. This article will describe how to test a car battery to determine how well it is holding up.

How to test a car battery with a multimeter

For cars with the engine in front, the battery is normally located in the engine compartment. For a mid or rear engine car, the battery may not be located in the engine compartment. To find the exact location it is a good idea to consult your car’s user manual.

Once you have located the battery, the first thing you will notice is that it has a positive (+) and a negative (-) terminal post. Each terminal will have a heavy cable connected to it. The positive terminal will usually have a protective cover which you will need to remove to expose the terminal post. The negative terminal post is usually unprotected.

In case the terminals are accessible, you can perform the car battery voltage test using the multimeter by following these steps:

Step 1: Set the meter to test DC voltage and use the 20V range setting.

Step 2: Touch the positive (red) probe to the positive battery terminal post.

Step 3: Touch the negative (black) probe to the negative battery terminal post.

Step 4: If you get a (-) in front of the voltage number then you have reversed the probes.

Step 5: Assuming a positive (+) voltage reading you should see an ideal voltage of 12.6 volts.

Step 6: If it’s slightly lower, don’t panic as car accessories draw on the battery even when the car is off.

Step 7: Refer to the chart below for a cross-reference of measured voltage vs. state of charge and status.

Car Battery Voltage Chart

Periodically measuring your battery voltage is a good way to identify how well your battery is holding up. The measured voltage will provide a good indication of the battery’s charge and potential for failure.

The “state of charge”, that is based on the measured voltage reading, tells you a lot about your batteries condition. Over time, the state of charge (%) will start to go down which indicates that the battery is becoming weaker. As it approaches the 70% point you may want to have the charging system checked by a professional. This step will identify whether any other system components are contributing to the low state of charge. Sometimes it is not a weak battery that is the problem but a component of the charging system that needs attention. Referring to the state of charge (%) may provide you with an early warning of charging system issues.

Measuring your battery voltage is a good way to identify how well your battery is holding up
Car Battery Voltage Chart.

How to tell if your car battery is bad?

In the how to test a car battery section, a multimeter was used to identify how well your battery is holding up. There are also other warning signs that you may notice which should not be ignored, such as:

  • Engine turns over slowly
  • A Check Engine Light comes on
  • The fluid level in one or more battery cells is low
  • The battery case looks bloated
  • There is a leak in the battery
  • The battery is more than 3 years old

If you do notice any of these warning signs then you need to take action immediately if not sooner. Usually, the battery will not fail all at once but takes its sweet time, sending out warnings along the way. If you are watching for these warning signs then you can take action before a complete failure occurs.

If you are not watching, you could become stranded out in the middle of no-where with a dead car. If you have a service like AAA then a battery is only a phone call away. If you don’t have service then your car will have to be towed and you’ll be without transportation for a while.  When it comes to car batteries, an ounce of prevention is worth a pound of cure, so don’t ignore the warning signs.