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?
When discussing car battery voltage, we’re generally talking about a 12-volt battery. When we take a closer look, we see car battery voltage can range anywhere from 12.6 to 14.4.
- With the engine off, the fully charged car battery voltage will measure 12.6 volts. This is known as “resting voltage.”
- When the engine is running, the battery voltage will typically rise to 13.5 to 14.5 volts. The battery is boosted to these higher levels by the alternator.
You must 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 which will unclip, hinge up, or occasionally require removing 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 Test A Car Battery With A Multimeter?
The first test with your multimeter will measure DC voltage, indicated with a solid line and a dashed line above a letter V. Set the dial to 20, which will allow you to accurately measure between 0-20 Volts.
Touch the red probe to the positive (usually red) terminal, and the black probe to the negative (black) terminal. The terminals will be marked + and -. If you get a reading with a minus in front of it (-12.6 rather than 12.6) you’ve got the probes the wrong way round!
The resting voltage should ideally be no lower than 12.6V. A battery that reads 12.2V is actually only 50% charged and is classed as discharged below 12V.
One thing to bear in mind is that all modern cars experience ‘parasitic loss’, which is when something electrical drains the battery even with the engine turned off. So, systems such as the clock, computer and alarm use some power. If you suspect this is killing your battery during storage, you might be wise to disconnect the battery or remove it entirely.
If the multimeter reads less than 12.6 volts, disconnect the battery and fully charge it using a battery charger. Then let it rest overnight. If it holds a charge when it’s not connected to the car – something is draining the battery far faster than the computer memory and digital clock.
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 over charging – 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).
Related Post: How To Test an Alternator with A Multimeter?
Detecting a Bad Cell
- A healthy cell will show ~2V, a damaged cell 1V or less.
- Test each cell individually, or groups of 2–3 cells in series.
- One low reading signifies that cell is bad and battery should be replaced.
Isolate bad cells causing voltage drains using a multimeter across individual banks.
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!