Knowing how to test a car battery is a valuable skill that can save you time and money down the line.
But how do you know when you should be testing your battery in the first place?
In this article, we’ll answer that question and show you how to test your battery with and without a battery tester. Then, we’ll go over some FAQs to give you a better understanding of testing a car battery.
This Article Contains:
(Click a link to jump to a specific section)
- How To Test A Car Battery With A Multimeter
- How To Test A Car Battery Without A Multimeter
- 4 Signs Of A Bad Battery
- 4 Car Battery FAQs
Let’s get started.
How To Test A Car Battery With A Multimeter
Using a multimeter is one of the most common ways for people to test their car battery.
You can grab one at your local hardware store for less than $10.
A couple of other car battery tester tools can also get the job done, like a voltmeter or power probe. However, a multimeter is your best bet since both a voltmeter and a power probe are more limited in their capabilities.
The process is quite simple, just follow these steps:
However, before testing your battery with a multimeter, voltmeter, or power probe, there are a few things to keep in mind.
1. These instructions are for what’s referred to as maintenance-free batteries.
These batteries don’t have plastic caps on each cell. If you have a battery that does have plastic caps, you’re going to need a hydrometer to test it, not a multimeter.
2. Always wear a pair of rubber gloves and goggles when working on your battery. This will protect your skin and eyes from battery acid.
With that taken care of, let’s get into how you can start testing your car battery:
Step 1. Remove The Surface Charge From The Battery
To do this, turn your headlights on for about two minutes. Don’t turn the car on, just the headlights. We do this because we need to test the battery’s resting voltage; otherwise, you can get a false reading as the battery might still be holding a charge from the alternator.
Step 2. Perform A Quick Visual Inspection
While you’re waiting with the headlights on, you can go ahead and give the battery a quick visual inspection. You want to look out for any corrosion buildup.
It usually looks like a white or yellow crust that forms around the battery terminal. Corrosion might even explain why you’re having battery issues in the first place.
If you see some corrosion, you can clean that off with a battery cleaning solution, like baking soda and water, or some fine sandpaper. For instructions on how to safely remove corrosion from your battery, read this guide.
While you’re there, double-check each battery cable is fastened correctly,
If everything looks alright, move ahead to the next step.
Step 3. Set Up Your Multimeter
Now that you’ve prepared the battery, you can start setting up your digital multimeter to test your battery’s voltage.
To do this, adjust it to about 20V of DC voltage. Setting it to 20V isn’t a must; the important thing is that it’s above 15V, so you get the correct reading. You can go ahead and turn your headlights off.
Step 4. Connect The Multimeter
Touch the probes on the digital multimeter to the corresponding points on the battery.
First, connect the negative point (black) on the multimeter to the negative terminal on the battery. Then connect the positive point (red) on the multimeter to the positive terminal on the battery.
Step 5. Check The Multimeter’s Display
When connected to a fully charged battery, the multimeter will highlight your battery’s voltage as being between 12.5V to 12.6V if everything is working as it should be.
Remember, the outside temperature and the type of battery you have will affect the battery voltage.
- For a standard lead acid battery at around 80℉ (27℃), a good battery that’s fully charged will be in the 12.2 – 12.6 volt range. Whereas a fully charged AGM battery will have an open circuit voltage of about 12.8V to 12.9V.
- At 30℉ (-1℃), the battery voltage will be around 12.58V and 12.51V.
- At 0℉ (-17℃), your volt reading will be a little less if you have a good battery.
For reference, a lead acid battery that’s about 75% charged will have a volt reading of around 12.45V. Anything below 12V suggests something is wrong with your battery and probably won’t start your car.
If the multimeter displays the battery’s voltage as anything between 12.3V and 12.5V, it could use a charge. If it doesn’t start at all, you can jump-start your car from someone else’s with a pair of jumper cables. Once your vehicle is running, the alternator can charge your battery. Alternatively, a battery charger will also work.
Anything below 12.2V suggests the battery’s resting voltage is weak and you’ll need a replacement.
Step 6. Turn On Your Car
Have someone else turn the car on while the digital multimeter is still attached.
The voltage reading should change, but the voltage drop shouldn’t go below 10V. If it does, your battery isn’t producing the correct voltage to power your car.
If you’re getting a large voltage drop, your best bet would be to organize a new battery.
However, if the readings are around 12.6V, you should have a good battery, and something like a bad alternator may be causing the issue.
But what should you do if you don’t have a multimeter available?
How To Test A Car Battery Without A Multimeter
While performing a battery test with a multimeter is the most efficient method, it’s not the only method.
If you don’t have a digital multimeter or another type of battery tester on hand, there are a few things to help figure out how your battery is performing.
1. Perform A Quick Visual Inspection
Make sure the battery isn’t leaking and it’s not bulging — your battery case should be a perfectly square box. Also, have a look for corrosion around each battery terminal and that each battery cable is connected securely.
If everything seems fine, move to the next step.
2. Test The Battery
Start by turning your car off and switching the headlights on. Leave them on for about 15 minutes.
3. Crank The Engine
After waiting around 15 minutes with the headlights on, crank the engine and see what happens. You’ll probably need some help here so you can keep an eye on each headlight. You might see your headlight dim slightly as you start your car; this is normal.
However, there are a few things that suggest you have a problem with your charging system:
- Your headlight gets much dimmer or turns off entirely
- The engine takes a while to turn over
- There’s a clicking noise
Bear in mind that this isn’t nearly as accurate as using a digital multimeter, but you can use it to tell if your battery is performing as it should.
If your car turns on fine and the headlights aren’t dimming, your charging system is probably functioning normally.
Having said all of that, how do you tell if you have a bad battery?
4 Signs Of A Bad Battery
Generally, you should conduct a car battery voltage test about twice a year to avoid total battery failure. However, there are several other signs to look out for to help avoid a dead car battery. Aside from corrosion, here are a few other symptoms:
1. Slow Engine Starting
This is often the first sign of battery failure.
When something’s not right, your battery will struggle to hold a full charge, which often manifests as a slow engine start.
The main reason for this is the battery not sending enough power to the starter motor to get the engine to turn over. If this is a common issue for you, there’s a good chance you’ll have a dead car battery fairly soon.
2. Dim Lights
As mentioned above, dimming lights is another good indicator that there’s something wrong with your battery, though this also refers to your interior lights.
You may also notice issues with another electrical component, like the power windows or radio, for example. An electrical component like this is more likely to fail altogether, while your lights will start dimming before they fail outright.
3. A Clicking Noise
If your battery can’t send enough power to the starter motor to turn your car on, you’ll likely hear a series of clicks. This will tell you that you have a dead battery and your car won’t start at all.
4. Battery Light On Your Dash
You may notice a battery indicator light on your dashboard when your battery starts acting up. Some cars will throw up a general check engine light, whereas others may show an image of a battery.
If that light is on in your dash and you’re noticing a few other symptoms, it’s a safe bet you’re dealing with battery failure and you’ll probably need a battery replacement.
Now let’s look at some FAQs to give you a better understanding of your car battery.
4 Car Battery FAQs
Here are the answers to a few general car battery questions:
1. What Is A Multimeter?
A multimeter is a simple battery tester used to measure volts (V), Amps (A), and resistance (Ω) from an electrical source. Most often, though, a multimeter is used to test the strength of a car battery.
Using it to test your car battery will give you an accurate voltage reading. A multimeter can also indicate how your battery holds up while powering several electrical components.
2. How Long Should My Car Battery Last?
Several factors affect your car battery’s lifespan. The first factor is time — batteries have a finite lifespan. Generally, batteries last between three and five years, but your driving habits and how long the car remains undriven can reduce that.
Some other factors that affect your battery’s lifespan include:
- Excessive heat
- The alternator
3. What Is A Load Test And How Do I Perform One?
A battery load test is a kind of battery test that involves measuring the amperes produced by a charged battery. Cold cranking amps (CCA) is the term used to describe the battery’s power.
Performing a load test helps determine if your battery is capable of powering the starter motor.
To perform a successful load test, you’re going to need a battery load tester.
You can pick a load tester up for about $20.
Here’s how you use it:
- Step 1 — Begin by fully charging the battery. You need to do this to ensure you get an accurate result. You can use a battery charger if you have one on hand. Use your multimeter to check if your battery voltage is the same as what’s indicated on the battery label.
- Step 2 — Then, make sure your multimeter is set to measure voltage and connect it to the battery. If the voltage reading is lower than 10% of what’s on the label, you’ll need to charge the battery before doing a load test.
- Step 3 — Now, you need to disconnect the multimeter from the battery.
- Step 4 — Examine the battery label again, this time looking for its ampere rating. You should notice a “CCA” followed by a number. This number indicates the cold cranking amps. Take that number and halve it to get to the figure for your load test. For example, if your CCA is 500, then 250 is the figure you’ll need.
- Step 5 — Connect the load tester’s sensors to each battery terminal, making sure to connect positive to the battery’s positive terminal and negative to the negative battery terminal.
Be sure to leave the sensors for at least 15 seconds.
Then, read the load tester and compare it to the number you calculated in step 4.
If the reading is 10 – 15% less than your calculated number, your battery can’t produce the power needed to get your engine running.
4. What’s An Easy Solution To My Car Battery Troubles?
If you find yourself with a faulty battery, you’re going to need a battery replacement.
Fortunately, RepairSmith can help you with all your vehicle repair and maintenance needs.
RepairSmith is a convenient mobile vehicle maintenance and repair solution. Here’s why you’ll want them handling your battery issues:
- Replacements and fixes can be performed in your driveway
- Professional, ASE-certified technicians perform the vehicle inspection and servicing
- Online booking is convenient and easy
- Competitive and upfront pricing
- Only high quality equipment, tools, and replacement parts are used in repairs
- RepairSmith offers a 12-month | 12,000-mile warranty on all repairs
Fill out this form for an accurate cost estimate of a car battery replacement and any other repairs.
Performing a battery test can help avoid a dead battery down the line.
Remember, as your battery ages, it’s going to start becoming less efficient and it’s helpful to know what those warning signs are.
And while it’s possible to replace a car battery yourself, it can be a bit complicated. If you’d prefer to leave it to the professionals, you can always rely on RepairSmith.
Just contact them, and their ASE-certified mechanics will be at your driveway to take care of all your car battery needs.