Having a no-start situation on your car is frustrating, and stressful. In most cases, you’re left wondering what’s actually going on with the vehicle, and culprit #1 tends to be the battery.
But other than searching “how to tell if car battery is dead,” how do you know if you can jump it or just need to replace it? How do you know if the battery is actually charged properly?
A cheap tool and a simple test with a multimeter can let you know if your battery is properly charged. There are options with multimeters from $20 to several hundred dollars, and they’re extremely helpful for any electrical work you need to do.
Learn the easy solutions to potential problems that can come with a bad battery with a multimeter, and here’s how you use it.
How many volts should a car battery have?
A healthy car battery should register about 12.6 volts. It’s important that you test the battery after it’s been sitting for at least an hour, to get what’s called the ‘resting voltage’.
If you’ve recently been for a drive (and as long as the charging system is working correctly) the battery is likely to give a higher reading than the resting voltage, which could be misleading.
Better still, leave the car overnight and test the battery in the morning to get a really accurate gauge of the state of charge.
Using a multimeter to test a battery is easy. The first thing to do is make sure you can access the battery terminals (the metal connections on the top or front of the battery).
Batteries are commonly located in the engine bay to one side of the engine. If the battery is not immediately obvious when you open the hood, consult the owner’s manual.
In modern cars, the battery will often have a plastic cover that will unclip, hinge up, or occasionally require removal with a few bolts or screws. There may also be a red cover over the positive (+) terminal that will lift off or snap open, too.
Once the battery is exposed, be extremely careful that nothing metal touches the terminals and causes a short, so don’t rest wrenches or other tools on top of the battery.
Related Post: How to Tell Positive and Negative Terminals on a Car Battery?
How to Use a Multimeter?
Essentially, a multimeter is a device to test electrical circuits for a variety of industries. It can be used for measuring current, voltage, resistance, continuity, and a gamut of other things.
There are analog multimeters still around, but the majority you’ll see available today are digital multimeters, with a small screen that displays your readings.
It has one black lead and one red lead that need to be connected or touched off to a point. You will be connecting the red lead to the positive terminal of the battery, and the black lead to the negative or ground terminal of the battery.
You will want to read your multi-meter manual to determine that the test leads are in the proper connecting spots on the meter for measuring voltage and continuity, and that the meter is set to DC voltage.
If your multimeter has increments, set it for the next number higher than the voltage you’re testing. For example, if your digital multimeter has settings for 2, 20, 200, and 2,000 volts, choose 20 since it’s the next highest number to the expected 12+ volts in a car battery.
Then, it’s a matter of attaching or touching the black lead to a ground source and probing your circuit with the red lead. Watch the display for your voltage reading.
How To Test A Car Battery With A Multimeter?
To measure battery load, conduct three voltage tests with the multimeter. Start the first test by making sure the vehicle is turned off. Multimeters have two probes: red and black.
The red probe is for contact with the positive terminal and the black probe is for contact with the negative terminal. Connect the multimeter’s red probe with the positive battery terminal and the black probe with the negative terminal.
The multimeter display should show a reading of 12.2 to 12.6 volts indicating a full charge. This voltage range means the battery is in good condition for starting the vehicle.
If the measured reading is less than 12.2 volts, the battery’s resting voltage is weak, which means it most likely needs to be charged or replaced.
Once the resting voltage has been determined, it is time to get a reading on the crank cycle.
This is the moment that the vehicle is turned on and the battery is under the most draw because of the higher amount of energy needed to drive the starter motor. To get this reading, a second person will be needed for the purpose of starting the ignition.
As soon as the car is turned on, the voltage reading will drop for a quick moment, but should not fall below 10 volts. If it falls below 10 volts, it means the battery does not have sufficient turnover strength and is prone to failure.
Again, in this case, recharge or replacement of the battery may be necessary.
Immediately following the crank cycle, the vehicle will begin to idle and maintain a steady draw from the battery. With the motor running, the multimeter rating should stay in the 14 to 14.5 volt range.
Dropping below 14 means either the battery is weak and unreliable for sustained vehicle operation or the alternator is failing. The alternator’s job is to generate energy to feed the electrical system and charge the battery while the vehicle is running.
Related Post: How to Charge a Car Battery?
Understanding Voltage Readings
Interpret voltmeter readings as:
- 12.4V to 12.7V — Fully charged and good condition battery.
- 12.2V to 12.3V — Low end of normal range. Retest under load.
- 12.0V — Borderline reading. Charge fully and retest.
- 11.8V or lower — Discharged battery. Will need replacement soon.
- 10V or lower — Extremely discharged. Battery likely faulty and should be replaced.
Voltage under 12V nearly always indicates a bad battery needing replacement.
How to check your alternator with a multimeter?
An alternator produces electricity and charges the battery. Not only that, but while you’re driving it also takes over and delivers power to the car’s electrical systems.
So with the engine running (and being mindful about moving parts) conduct the same battery test as above with your multimeter. A healthy charging system should give a reading of between 13.8V and 14.4V at regular idle speed.
Anywhere outside that range and your car’s either under, or overcharging – both of which will shorten the battery life and require further investigation. For more on the charging system in your car, see When Good Alternators Go Bad (and Why).
How to find dead cells in a car battery
First things first, knowing a battery cell is dead is of no more use to you than knowing that the battery won’t hold a 12.6 volt charge, because you can’t fix it. So, a test of the resting voltage is just as effective a diagnosis.
A battery usually won’t go bad all at once; instead, some of the cells that make up the battery will go dead. An engine that’s slow to turn over when starting is often a sign of dead battery cells.
Most new car batteries are of the sealed ‘maintenance free’ variety, but some older batteries allow you to access the individual cells. The cells will either have individual caps, or a plastic cover that clips over all, or several of the cells. The cells contain a mix of water and sulfuric acid, so make sure you don’t get any liquid on your skin.
To test each cell, you need a hydrometer-style battery tester that measures the specific gravity of the battery acid. Based on the number of balls floating, you can tell whether the cell is dead or not.
Pro Tip: Before you disconnect your battery make sure you know the anti-theft code for your stereo – you may find it won’t work when you reconnect it otherwise!
Related Post: How To Test an Alternator with A Multimeter?
Tips for Accurate Voltage Testing
Follow these tips for reliable results testing battery voltage:
- Maintain secure lead connections — clean terminals thoroughly first
- Make sure ignition and all accessories are OFF while testing resting voltage
- Retest alternately at negative and positive terminals for complete context
- Repeat tests under various loads to simulate real world conditions
- Test consistently over time and track changes to identify failing batteries
With practice, you will become adept at diagnosing battery issues quickly through voltage and load testing.
How Much Voltage Does A Car Battery Need?
A battery needs the bulk of its voltage in order to function properly. While some people think that a battery has to get down to zero volts before it stops working, the reality is that a car battery can’t dip too far below 12 volts before it’s unable to perform its duties and turn your vehicle on.
Here’s a car battery voltage chart that correlates a battery’s voltage to its life, to help display how many volts are really needed to keep your car running happily.
| Voltage | State of the Battery’s Charge |
| 12.6 or higher | 100% |
| 12.5 | 90% |
| 12.42 | 80% |
| 12.32 | 70% |
| 12.2 | 60% |
| 12.06 | 50% |
| 11.9 | 40% |
| 11.75 | 30% |
| 11.58 | 20% |
| 11.31 | 10% |
| 10.5 or lower | Dead |
Related Post: How Much Should A Car Battery Cost?
FAQs.
What is a Multimeter?
A multimeter measures the voltage in your car battery, letting you know how much power is currently stored in the battery.
How Do I Know if My Car Battery is Bad?
The most common symptoms that come with a bad battery include:
1. Battery light illuminated on the dashboard
2. Engine cranks slowly when starting
3. Vehicle requires frequent jump starts
4. Clicking when you turn the engine
5. Lights are dim
6. Car won’t start
How Long Should a Car Battery Last?
Most car batteries are warranted to last for four years, but only around 30% of batteries made today make it to that point.
What Else Could Be Wrong with My Car Battery?
Another common problem with your car battery is corrosion at the terminal connections. You can remove the corrosion with sandpaper, but make sure to wear gloves and safety goggles!