How to check the battery with a multimeter
Content
A dead battery is one of the most common problems that a car owner faces. A battery test is needed to decide if a battery needs to be replaced.
It is often difficult to diagnose a problem. A cheap tool like a digital multimeter can test a battery and tell you if its car battery is holding a charge. The multimeter can also test alternators, which can negatively impact your battery.
In this article, we will help you determine the health of the battery using a multimeter, as well as answer the following questions:
- How do I know if my car battery is dead?
- Generally, what is the battery life?
- In what situations is it not recommended to use a multimeter to test a car battery?
How many volts are in a car battery?
After testing the battery, the ideal voltage across the car battery should be 12.6 volts. Anything below 12 volts is considered a dead or depleted battery.
Steps to test a car battery with a multimeter
Testing batteries with a multimeter is a relatively simple and well thought out process. The result indicates either that the car battery needs to be charged, or that it is time to replace the old one.
1. Remove residual charge
Leave the machine running for at least an hour before checking the battery. This will help you get the most accurate battery voltage reading.
If this is not possible, turn on the headlights for a few minutes with the vehicle turned off. This will eliminate any residual charge your vehicle's electrical system may have.
2. Prepare your multimeter
Make sure you get the correct value for how many volts of electricity your car battery can produce by setting the digital multimeter to 20 volts. Select the lowest voltage above 15 volts on your DMM if your DMM does not have this voltage.
3. Find a car battery
To test a car battery, you need to first make sure you can locate the battery and its terminals. In most vehicles, the battery is located under the hood in the engine compartment on one side of the engine. However, there may be batteries in the trunk of modern cars. If you can't find it, you can refer to your car owner's manual or the car manufacturer's website to locate it.
Batteries in modern cars have a plastic cover that you may have to unscrew to gain access to the battery terminals. Make sure that no metal objects, such as tools, come into contact with the terminals, as they may shorten.
4. Connect the multimeter leads to the battery terminals.
Connect each DMM lead 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 will be black, and the positive terminal and probe will be red. If you are not getting a positive DMM reading, you need to reverse them.
While some probes are metal pieces that can be touched, some are clamps that must be attached.
5. Check reading
The multimeter will show you the reading. Please write it down. Ideally, even after turning on the headlights for 2 minutes, the voltage should be close to 12.6 volts, otherwise you may have a bad battery. If the voltage value is slightly higher than 12.6 volts, then this is completely normal. If the battery drops to 12.2 volts, it is only 50% charged.
Anything below 12 volts is called dead or discharged.
Even if your battery is well charged, it is wise to check if the car can successfully consume power.
6. Have someone start the engine
Next, with the multimeter leads attached to the car battery, ask a friend to turn on the car's ignition. Before starting the vehicle, make sure the vehicle is in neutral and the parking brake is on. In addition, any multimeter lead must not hang from moving belts or motor pulleys.
This is a job for two people; one should monitor the oscillations of the multimeter, and the other should control the ignition. Try not to do all this yourself, otherwise you may record incorrect readings.
7. Check your reading again
Ideally, when the car tries to start, the voltage should first drop to 10 volts. If the reading drops below 10 volts but stays above 5 volts, the battery will slowly and soon die. If it drops another 5 volts, it's time to change.
Further, when the engine starts, the generator will give out current, and the battery readings will begin to rise again. The reading will return to a higher value of about 14 volts under ideal conditions. (1)
Any value outside this range indicates either an undercharged or overcharged battery. Hence, the alternator must be inspected otherwise it will ruin your vehicle's battery.
What are the symptoms of a bad car battery?
You may experience the following issues that indicate a bad battery:
- Low battery on dashboard display
- Engine click when turning on the car
- The need for frequent jumping
- Delayed ignition
- Headlights do not turn on, are dim and cannot withstand operation for 2 minutes.
How long should a car battery last?
Most car batteries have a four-year warranty, but they may not last that long. Usually they serve 3-4 years, after which they must be replaced with new ones.
When can't I use a multimeter to test a car battery?
If you don't have maintenance-free batteries, you can use a hydrometer to test these car batteries. If you want to identify them, maintenance-free batteries have plastic caps on each cell. (2)
The final verdict
You don't need professional help to complete the steps above, and checking your battery with a multimeter is one of the easiest and cheapest ways.
Recommendations
(1) Alternator – https://auto.howstuffworks.com/alternator1.htm
(2) hydrometer - https://www.thoughtco.com/definition-of-hydrometer-605226
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