Last Updated on September 18, 2020
Running into a dead battery is one of the most common problems that a car owner experiences. To decide whether a battery replacement is needed or not, a battery test is necessary. Many a time, it can be challenging to diagnose the issue. A cheap tool such as a digital multimeter—can test the battery and let you know if your car battery is holding any charge. A multimeter can also be used to check alternators that may be adversely affecting your battery.
In this article, we help you identify the health of the battery with the multimeter, along with providing answers to the following questions:
- How do I know the car’s battery has gone bad?
- Typically, what is the life of a battery?
- In what situations, it is not ideal to use a multimeter to check the car’s battery?
Also known as multitester or VOM, a multimeter is an electronic device used to measure various electrical quantities like voltage, current, and resistance. Here, we’ll use it as a voltmeter to measure the voltage across the car battery. Fluke and Klein are some of the brands that produces the best multimeter now in the market.
How Many Volts Are in a Car Battery?
After battery testing, the value of ideal voltage across a car battery should be 12.6 volts. Anything lower than 12 volts is considered a discharged or dead battery.
Steps to Test a Car Battery with a Multimeter
The testing of batteries with a multimeter is a relatively easy and well-versed process. The result either tells you to charge your car battery or that it is time to replace the old one.
1. Remove residual charge
Before testing battery, leave the car running for an hour, minimum. This would help you get the most accurate reading of the battery’s voltage.
In case it is not possible, then turn on the headlights for a few minutes with the vehicle off. This would get rid of any residual charge that your car’s electrical system may have.
2. Prepare your multimeter
Make sure to get the correct reading for how many volts of electricity your car battery can produce by setting your digital multimeter to 20 volts. If your multimeter doesn’t have that voltage, then select the lowest voltage above 15 volts on your digital multimeter.
3. Find the car battery
To test a car battery, you’ll need to make sure that you can find the battery and its terminals first. In most vehicles, the battery is located under the hood in the engine bay towards one side of the engine. However, modern cars may have batteries in their trunk. If you cannot find it, then you may consult the automobile’s manual or the car manufacturer’s website to determine the location.
The present-day cars have a plastic cover over their batteries that you may need to unscrew to access the battery’s terminals. Make sure to prevent anything metal, like tools, from touching the terminals, since it may shorten.
4. Connect the multimeter probes to the battery terminals
Connect each probe of the digital multimeter to the car battery terminals, negative to negative and positive to positive. Both—the multimeter and the battery—are color-coded. The negative terminal and probe are black, and the positive terminal and probe will be red. If you are not getting a positive reading in the digital multimeter, you need to reverse them.
While some probes are metal pieces to touch, some are clips that are to be attached.
5. Check the reading
The multimeter will show you the reading. Please write it down. Ideally, even after running the headlights for 2 minutes, the voltage should read close to 12.6 volts, or you may have a bad battery. If the voltage value is slightly higher than 12.6 volts, then it’s perfectly normal. If the battery goes down to 12.2 volts, then it’s only 50% charged.
Anything lower than 12 volts is termed as dead or discharged.
Even if your battery doesn’t have a bad charge, it’s wise to check if the car can draw power successfully.
6. Ask someone to fire up the engine
Next, keeping the multimeter probes attached with the car battery, ask a friend to turn the car’s ignition. Make sure that the vehicle is in neutral and the parking brake is engaged before starting the car. Also, any multimeter wire must not be hanging into any moving belts or pulleys on the engine.
This is a two-people job, one must keep an eye on the multimeter for the fluctuations, and the other must take control of the ignition. Try not to do it all by yourself, or else you may end up recording an incorrect reading.
7. Check the reading again
Ideally, as the car tries to start, the voltage must initially drop to 10 volts. If the reading falls below 10 volts but stays above 5 volts then, that means the battery is slowly dying and will soon be dead. In case it drops further down 5 volts, then it is time to bring around a new one.
Next, when the engine starts to run, the alternator will produce a current, and the battery reading will begin to rise again. In an ideal condition, the reading will return to a higher value of around 14 volts. (1)
Anywhere outside this range indicates either an under-charged or over-charged battery. Hence, the alternator must be looked into, or it’ll ruin your car’s battery.
What Are the Symptoms of a Bad Car Battery?
You might face the following issues that point towards a busted battery:
- Low battery level on the dashboard display
- Clicking of the engine when the car is turned on
- The need for frequent jump starts
- Delayed ignition
- Headlights won’t turn on, are dim, won’t sustain for running for 2 minutes
How Long Should a Car Battery Last?
Most car batteries have a warranty of four years, but they might not last that long. They tend to function for 3-4 years before needing to be replaced with a new one.
When Can I Not Use Multimeter to Test a Car Battery?
If you do not have maintenance-free batteries, you can use a hydrometer to test such types of car batteries. In case you want to identify them, maintenance-free batteries have plastic caps on every individual cell. (2)
You do not need professional help to perform the above steps and to test a battery with a multimeter is one of the easiest and cheapest ways.
(1) alternator – https://auto.howstuffworks.com/alternator1.htm
(2) hydrometer – https://www.thoughtco.com/definition-of-hydrometer-605226