Knowing how to test a car battery is a valuable part of car maintenance that can save you time and money down the line.
But how do you know when to test your battery?
Read on to know how to test your battery health with and without a battery tester. We’ll also explore the warning signs of a battery issue and some finer details related to the car battery testing process.
This Article Contains:
- How to Test a Car Battery With a Multimeter
- How to Test a Car Battery Without a Multimeter
- How to Test a Car Battery With a Hydrometer
- 4 Signs of a Bad Battery
- 4 FAQs about Car Batteries
How to Test a Car Battery With a Multimeter
Using a multimeter is one of the most common ways to test your car battery.
Some other tester tools for car batteries, like a voltmeter or power probe, can also get the job done. However, a multimeter is your best bet since voltmeters and power probes are limited in their capabilities to test battery health.
The process is as follows:
- Remove the surface charge from the battery
- Perform a quick visual inspection
- Set up your multimeter
- Connect the multimeter
- Check the multimeter’s display
- Turn on your car
But wait!
Here’s what you should know before testing your battery with a multimeter:
- These instructions are for maintenance-free batteries that don’t have plastic caps on each cell. Most modern cars offer these maintenance-free batteries. If you have a battery with plastic caps, you can use a hydrometer to test it.
- Wear rubber gloves and goggles when working on your battery to protect your skin and eyes from battery acid.
Note: If you don’t have access to these tools or are not confident with car parts, have a mechanic test the battery for you.
If you still wish to do it yourself, here’s how you can start testing your car battery life:
Step 1: Remove the Surface Charge from the Battery
Turn your headlights on (while the car’s off) for about two minutes to remove the surface charge from the battery. Doing so helps test the battery’s resting voltage. Otherwise, you can get a false reading since the battery might hold a charge from the alternator.
Step 2: Perform a Quick Visual Inspection
Give the battery a visual examination. Look for corrosion buildup (white or yellow crust around the battery terminals) — it could affect battery performance.
You can clean corrosion off with a fine sandpaper or battery-cleaning solution, like baking soda and water. But don’t forget to disconnect the battery first to avoid getting an electric shock. Disconnect the negative terminal followed by the positive.
Double-check that you’ve fastened each battery cable correctly.
Step 3: Set up Your Multimeter
Set up your digital multimeter to test your battery’s voltage. To do this, adjust it to a DC voltage of about 20V (or at least above a DC voltage of 15V for a correct reading).
You can turn your headlights off.
Step 4: Connect the Multimeter
Connect the probes on the digital multimeter to the corresponding points on the battery.
First, connect the negative multimeter cable (black probe) to the negative terminal on the battery. Then, connect the positive multimeter point (red probe) 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 car battery voltage from 12.5V to 12.6V if everything is working as it should be.
Remember, the surrounding climates and battery type affect your battery’s voltage.
For example:
- For a standard lead acid battery at around 80℉ (27℃), a fully charged battery will be in the 12.5V to 12.6V range. A fully charged AGM battery will have an open circuit voltage of about 12.8V to 13V.
- At 30℉ (-1℃), the battery voltage will be around 12.588V.
- At 0℉ (-17℃), your volt reading will be 12.516V if you have a good battery.
For reference, a lead acid battery that’s about 75% charged will have a volt reading of around 12.4V.
If the multimeter displays the battery’s voltage between 12.3V and 12.5V, it needs recharging.
If it doesn’t start, you can jump-start your car using someone else’s charged car battery. Once your vehicle is running, the alternator can recharge your battery. Alternatively, a battery charger suited to your car battery type will also work.
Anything below 12.2V implies that the battery’s resting voltage is weak, and you must get a battery 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 large voltage drops, it would be best to get a new battery.
However, readings around 12.6V indicate a healthy battery and something like a bad alternator might be causing the issue.
But what can you do if you don’t have a multimeter?
How to Test a Car Battery Without a Multimeter
Although a multimeter is the most efficient method for car battery testing, it’s not the only method. If you don’t have a digital multimeter or another type of battery tester on hand, follow these steps:
Step 1: Perform a Quick Visual Inspection
Ensure the battery isn’t leaking or bulging — your battery case should be a perfectly square box. Look for corrosion around your battery terminals and ensure each battery cable is connected securely.
Step 2: Test the Battery
Turn your car off and switch the headlights on. Leave them on for about 15 minutes.
Step3: Crank the Engine
After waiting, crank the engine and keep an eye on each headlight. You might see your headlight dim a little as you start your car. This is normal.
However, your charging system may have a problem if:
- Your headlight gets much dimmer or turns off entirely
- The engine takes a while to turn over
- There’s a clicking noise
If your car turns on fine and the headlights aren’t dimming, you mostly have a healthy battery and charging system.
Step 4: Use a Virtual Battery Tester (Optional)
You can also use an online battery tester to estimate your car battery’s health.
It’ll estimate your battery capacity, age, and how long it is expected to last based on the following details:
- Vehicle’s make and model
- Car’s year of manufacture
- Region of use
- Vehicle’s engine type
Do you have a car battery with removable caps on the cells?
You can use a hydrometer to test it.
How to Test a Car Battery With a Hydrometer
Hydrometers can be used to test batteries with accessible electrolytes. These assess battery health by measuring the specific gravity of the electrolyte in lead-acid batteries.
Here are the steps you can follow:
- Eliminate any surface charge by turning on the headlights (as mentioned above).
- Use a screwdriver to open the plastic vent caps on the battery.
- Insert the hydrometer’s nozzle into your battery’s electrolyte solution.
- Extract a tiny sample of the electrolyte into the hydrometer.
- Check the specific gravity reading on your hydrometer’s scale based on the chart below.
| Specific Gravity | State of Charge |
| 1.300 | 100% |
| 1.255 | 75% |
| 1.215 | 50% |
| 1.180 | 25% |
| 1.160 | 0% |
Note: You can’t use a hydrometer to test a sealed, maintenance-free, or AGM battery.
Next, let’s see how you can tell if you have a bad battery.
4 Signs of a Bad Battery
You should typically conduct a car battery voltage test about twice a year to avoid total battery failure.
However, you might have a weak car battery if you notice these signs:
1. Slow Engine Starting
Vehicle battery failure often manifests as a slow engine start since the battery struggles to hold a full charge.
The main reason for this is the battery not sending enough power to the starter motor for 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 or Flickering Lights
Your lights will start dimming before the battery fails. You may also notice issues with other electrical components, like the power windows or radio.
3. 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 indicates that you have a dead battery, and your car won’t start.
4. Lit Battery Light on Your Dash
You may notice an illuminated battery indicator light on your dashboard when your battery starts acting up. While some cars will throw up a general check engine light, others may show an image of a battery.
If this light is active on your dash and you notice a few other symptoms, you’re likely dealing with battery failure. You’ll probably need a battery replacement.
Still have doubts about car batteries?
4 FAQs about Car Batteries
Here are answers to a few general queries about car batteries:
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. You can use it to test the strength of car batteries, as it’ll 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?
Generally, a new battery will last between three and five years. However, your driving habits and how long the car remains undriven can reduce the battery capacity.
Other factors that affect your battery’s lifespan include:
- Excessive heat
- Cold weather
- Car vibrations
- Alternator issues
3. How Do I Know When My Battery Needs to Charge?
Here’s a battery voltage guideline on when you need to charge your car battery:
- 12.6V or more: 100% charged
- 12.4V: 75% charged
- 12.2V: 50% (needs to charge)
- 12V: 25% (needs to charge)
- < 12V: Fully discharged (dead battery)
4. How Do I Perform a Load Test?
A battery load test is a battery testing process that involves measuring the amperes produced by a charged battery. Cold Cranking Amps (CCA) is the term used to describe the ability of a battery to crank an engine in cold temperatures.
Performing a load test helps determine if your battery can power up the starter motor based on the cold cranking amp rating.
You’ll need a battery load tester for a successful DIY load test. If you don’t have one, you can let a mechanic do the test.
Here’s what they’ll do:
- They’ll use a multimeter to check if the voltage matches the figure mentioned on the battery label. If the voltage reading is lower than 10% of what’s on the label, they will charge the battery (using a battery charger) before doing a load test to ensure an accurate result.
- Disconnect the multimeter from the battery.
- Look for the battery’s ampere rating (cold cranking amps or CCA rating). Take that number and halve it to get to the figure for the load test. For example, if the cold cranking amp rating is 500, then 250 is the figure you’ll need.
- Set the load tester to this reading and connect the sensors of the load tester to the battery terminals. Connect the positive to the battery’s positive terminal and the negative to the negative battery terminal.
- Activate the tester and leave it connected to the battery for at least 15 seconds to apply the load to the battery.
- Read the load tester and compare it to the number calculated in step 4. If the reading is 10% less than the calculated number, the battery can’t produce the power required to run the automotive engine.
Fix Any Car Battery Issue with AutoNation Mobile Service
As your battery ages, it’ll start becoming less efficient. Knowing the warning signs and performing a battery test can help avoid a dead battery.
However, if you need a car battery replacement, you can rely on AutoNation Mobile Service.
We’re a mobile auto repair and car maintenance company offering upfront pricing and a 12-month, 12,000-mile repair warranty on all auto parts.
Contact us to get a car battery replacement or fix any battery problem from your driveway.