Multimeters have become a popular household need with so many battery-operated products in the house, and one of the most common applications is battery testing. A dead battery can ruin your morning or experience in the wild since testing your battery can help you determine if your battery is healthy enough to make a trip and if the slow starting has been caused by the car battery voltage or another issue.
What is a Multimeter?
A multimeter, also known as a VOM or multitester, is an electronic device that measures different electrical quantities like current, voltage, and resistance. The most common application of the multimeter measures the strength of a car's battery, and when used properly, it can provide voltage information with maximum accuracy on a digital readout. First, however, you should understand the data provided to know how strong your battery is and if it should be replaced.
How To Know If Your Vehicle’s Battery is Bad?
The most common symptoms that come with a bad battery and will include:
- Low battery level on your vehicle dashboard display
- Headlights may not turn on and will be dim and can't sustain running for even two minutes
- The vehicle engine clicking when you turn your car on
- Delayed ignition
- Often needing frequent jump starts
- Interior lights may turn on, but the car won't start.
How To Test Your Car Battery With a Multimeter
Testing your car batteries is an easy and straightforward process, and the result will determine if you should charge your car battery using a multimeter or you might have to replace it.
1. Remove Residual/ Surface Charge
Before you test your battery, you should leave your car running for about an hour minimum, and this should help you get the most accurate reading of your battery voltage. However, if not possible, you should turn the headlights on for a few minutes with your vehicle off, and this will also get rid of any residual charge your vehicle's electrical system may have.
The surface charge is a higher-than-usual charge on the battery plates surfaces and is usually present if the vehicle has just been driven or the battery has just been charged.
2. Prepare your Multimeter
How to test a car battery starts with having a multimeter, and the first step is setting your multimeter to voltage and ensuring it has been adjusted to 20 volts. If your voltmeter lacks incremental settings or lacks the voltage, you should set it to DC volts.
3. Find your Car’s Battery
To test your cars' batteries, you should know where your battery is located, with most vehicles having their battery under the hood in the engine bay and on one side of the engine. However, modern cars may have batteries in their trunk and if you can't find your battery, consult your mechanic or the car's manufacturer's website to determine the location.
Today's vehicles have a plastic cover covering their batteries, and you may need to unscrew the cover to access the battery's terminals. Avoid anything metal such as tools from touching your terminals as they may shorten it.
4. Touch the Probes to Battery Terminals
You should press each probe to its correct terminal where it's touching negative to negative and positive to positive. Your battery and voltmeter are color-coded, and a negative terminal and probe will be black while a positive terminal and the probe will be red. If you are not getting a positive reading in your digital multimeter, you will need to reverse them and remember, while some probes are metal pieces when you touch, some are attached clips.
5. Check the Reading
Your multimeter should show you the reading, and you should record it. Generally, your voltage should read close to 12.6 volts after running your headlights for two minutes, and if your voltage value is over 12.6, then it's normal, but if your battery goes down to 12.2 volts, then it shows only 50% charged.
Any reading lower than 12 is considered dead or discharged, and even if your battery doesn't have a bad charge, you should check if your car can successfully draw power.
6. Ask someone to fire up the engine
While the black probe and red probe are attached to your car's battery, you can ensure that your vehicle is in a neutral position and that the parking brake is not engaged for the starter. This job should be done by two people where one must observe the voltmeter for any fluctuations, and the other should control the ignition.
7. Check your Reading Again
As the car is trying to start, the voltage will initially drop to 10 volts, and if the reading reads below 10 volts, then it means that your battery is dying slowly, and it will soon be fully dead. When your engine starts to run, the alternator will produce a current, and the battery reading will start to rise again, and the best condition will have the reading return to a high value of about 14 volts.
How Many Volts Should a Fully Charged Battery Have?
Your vehicle uses a 12-volt battery, and therefore, a multimeter should read between 12.5 and 12.8 if the battery is healthy. Due to the way batteries discharge, it's important to test your battery after sitting for an hour to determine the resting voltage.
Leave your car overnight and ensure you test the car before starting it in the morning to get an accurate gauge of your car battery's health. Additionally, suppose you have been on a recent trip, and the charging system is working correctly. In that case, the battery is likely to give you a higher reading than the resting voltage, and it could be misleading.
What Causes a Car Battery to Drain?
Some of the possible cause that will cause your battery's charge to drain include:
- Poor battery connections
- Extreme weather
- A faulty charging system
- A short in your system
- Something such as a dome light is leeching power
Frequently Asked Questions on How to Test a Battery with a Multimeter
1. Will a Dead Battery Always Jump Start?
If there's nothing wrong with the battery, it should start, but when it has not been used for a while, all kinds of issues could come up, including corrosion that could cause a battery to be short and damage it. A bad battery will not jumpstart, but it should work well if it's low on charge.
2. Can a Bad Alternator Destroy a New Battery?
Yes, a bad alternator could cause your battery to overcharge and therefore destroying it.
3. When Can I Not Use Multimeter to Test a Car Battery?
If you are not using maintenance-free batteries, you should use a hydrometer to check them and identify them, and the maintenance-free batteries come with a plastic cap on each cell.