Knowing your battery voltage helps you determine how long it’s going to last.
In this article, we’ll answer that question and show you how to test your car battery voltage (with and without a tester). We’ll also tell you how to check your alternator and offer a quick solution to battery testing issues.
We’ll also cover some FAQs to give you a better understanding of car battery voltage and testing.
This Article Contains:
- What Should My Car Battery Voltage Be?
- How To Measure Car Battery Voltage
- How To The Check Car Battery Without A Tester
- How To Check The Alternator
- 9 Car Battery Voltage FAQs
Let’s get to it.
What Should My Car Battery Voltage Be?
The standard automotive battery is a 12 Volt battery.
The resting voltage (when the engine is off) measures around 12.6 volts. Car batteries typically provide these 12.6 volts through six cells, each supplying around 2.1V.
When the engine is running, the batterys voltage should fall between 13.7-14.7V.
But what does the voltage tell you?
Measuring the resting voltage can indicate the battery’s state of charge — or how much battery charge capacity remains.
In general, for a car battery with 12 volts, the state of charge is:
- 75% at 12.4V
- 50% at 12.2V
- 25% at 12.0V
- Considered fully discharged at 11.9 minimum voltage.
Note: If you’re curious as to whether 8 x 1.5V AA batteries are the same as the 12 volts in a car battery, the answer is no. AA batteries have too much internal resistance to kick-start a car.
Next, let’s look at a simple battery test for voltage measurements.
How To Measure Car Battery Voltage
For measuring the battery voltage and load, the multimeter has two probes: red and black. The red probe is for contact on the positive terminal, and the black probe is for the negative terminal.
Follow these six simple steps to measure the battery voltage:
- Turn Off The Ignition
- Set up The Tester To Measure DC
- Touch The Probes To Each Battery Terminal
- Check Voltage With Engine Off
- Do A Crank Cycle Test
- Measure Voltage With Engine On
Before you begin your battery test, here are a couple of pointers for safety and accuracy:
- Check the terminals for corrosion, as it can increase internal resistance and decrease the voltage reading (check out our guide to cleaning corrosion here).
- Check the battery for leakage, bloating, or damage — don’t work on the battery if the terminals are damaged. An AGM battery will ensure that no leakage can occur.
- Don’t smoke around batteries, as sparks can trigger an explosion.
- Wear safety glasses and gloves to protect yourself from battery acid in case of any mishaps.
Note: For a more accurate reading, it’s best to do a battery test 12 hours after turning off your vehicle. This allows any surface charge to dissipate. Otherwise, your readings could be higher than they should be.
Once that’s done, here’s what you need to do:
1. Turn Off The Ignition
Make sure your vehicle’s ignition is off.
To help remove the surface charge, you can turn on the headlights for 2 minutes. Ensure the headlights are switched off before you test the battery capacity.
2. Set Up The Tester To Measure DC
Set your voltmeter or multimeter setting to test DC or DC voltage (Direct Current Voltage).
If there’s a DC voltage range, set the maximum to read around 20-25V.
3. Touch The Probes To Each Battery Terminal
Locate the positive terminal (+) and the negative terminal (-) on the battery.
Sometimes the battery post is covered with a plastic cap. You’ll have to uncover the terminal to test, but you won’t have to remove the battery cables.
Your battery tester will likely have a red (+) and black (-) probe:
- First, touch the red probe (+) to the positive battery terminal
- Then, touch the black probe (-) to the negative battery terminal
Note: If you get a negative reading, it means your probes are swapped, and you just need to switch the battery post they’re touching.
4. Check Voltage With Engine Off
A good battery should have a resting voltage between 12.4-12.9V.
If the reading is less than 12.4V, it doesn’t necessarily mean you have a bad lead acid battery, just low voltage. Some electrical system might have drained it, or your alternator has trouble charging.
If the battery voltage is below 12.2V, it needs to be recharged. Try driving your vehicle for at least 15 minutes to bring the low voltage back up. Alternatively, you can buy car battery chargers to charge the battery back to its minimum voltage.
After recharging the low voltage battery, test it again to see if it holds the charge.
If the batterys voltage is over 12.9V, then your car battery has excessive voltage. Turn on your high beam to drain it. This could mean your alternator had overcharging issues.
Note: An AGM battery may display a higher voltage. Check the manufacturer datasheet for details.
5. Do A Crank Cycle Test
The crank cycle test shows how well the battery performs when delivering voltage to the starter motor.
Get a friend (or use a remote starter if you have one) to start the car.
There’ll be a quick voltage drop as the engine is cranking, and then it will rise again. The voltage drop shouldn’t go under 9.6V. If it does, it means the battery doesn’t have enough turnover strength, and you’ll likely need a new battery.
6. Measure Voltage With Engine On
With the engine on, your vehicle will idle, maintaining a steady draw from the battery.
The alternator will now charge the car battery.
You can expect to see the battery voltage measure around 13.7-14.7V. If the voltage reading is significantly lower or higher, it could mean issues with the battery or alternator.
But what if you don’t have a volt meter?
Can you still check your battery condition?
How To The Check Car Battery Without A Tester
While you can’t accurately measure voltage without a tester, you can still gauge the car’s battery condition.
Here’s what to do:
- With the engine off, turn on the headlights — they will be your test indicator
- Get a friend to start the car (or use a remote starter)
- Watch the headlights as the engine cranks
If the headlights dim during cranking, there might not be enough battery charge.
If the headlights remain steady, but the engine won’t start, then there’s no battery issue, but possibly a problem with the starter motor.
What about the alternator?
Is there a way to check it too?
How To Check The Alternator
The alternator is part of your vehicle’s charging system.
Here’s how to check if it’s working fine:
A. With A Tester
With the engine running, turn on all the vehicle’s electronics — headlights, interior lamps, stereo, etc. — to maximize the voltage load.
Now, measure the battery voltage.
If the charging voltage drop is under 13.5V, it means the alternator has trouble charging the car battery, and you should get a mechanic to look at it.
B. Without A Tester
If you don’t have a tester handy, you can still test the alternator.
Make sure the car is “Park” and the parking brake is on before you begin.
Start the engine without the headlights, then turn on the headlights:
- If the headlights are dimmer than usual, there might not be enough charging voltage from the alternator, so the headlights are running off sole battery power.
Now, rev the engine:
- If the headlights brighten, the alternator is charging the car battery but not providing enough voltage at idle.
- If the headlights remain the same, then there’s probably no alternator issue.
Turn on the interior lights:
- If they dim gradually with a running engine, there could be an alternator problem. Get a mechanic to verify the issue.
Now let’s go over some FAQs about car battery voltage.
9 Car Battery Voltage FAQs
Here are answers to some common car battery questions.
1. What’s A Voltmeter?
The voltmeter (or volt meter) is a simple instrument for measuring the electrical potential difference between two points in an electric circuit. Electric potential difference refers to the electromotive force of the battery.
2. What’s A Multimeter?
The multimeter measures multiple electrical properties — typically voltage (Volt), resistance (Ohms), and current (Amps). It’s sometimes called a Volt Ohm Milliammeter (VOM).
It is used to test if your battery has low or excessive voltage.
You can use a digital multimeter or an analog multimeter.
3. What’s The Alternator?
The alternator converts mechanical energy from the engine into electrical current for the car battery. It’s the primary element in your vehicle’s charging system.
Generally, the alternator produces more current at higher speeds which means that driving faster will produce more current.
There’s a cap, of course, on how much current the alternator can generate.
4. How Often Should I Test Battery Voltage?
You should check your battery voltage at least twice annually. This will give you an idea of its condition, so you’ll know when to bring it for further testing or if you need a battery replacement.
5. When Should I Use A Car Battery Charger?
Hook your battery to car battery chargers if the voltmeter reading dips under 12.4V.
If the reading is below 12.2V, you should consider using a trickle charger which charges at a much slower rate. Using a trickle charger helps avoid the risk of battery overheating and overcharging.
6. What’s A Car Battery Load Test?
The battery load test is used to test the 12 volt battery under load and is a more accurate battery health indicator than voltage measurement.
A load tester is specifically designed to determine the voltage generated while a load is placed on the fully charged battery.
During this test, the fully charged battery should be loaded with one-half of its cold cranking amp (CCA) rating at 70°F (or more.) A cold cranking amp refers to the battery’s ability to start in cold temperatures.
A good battery will be able to maintain 9.6V for 15 seconds with this load. If the load tester dips below 9.6V during the load test, it might be time for a battery replacement.
7. How Do I Know If I Have A Bad Battery?
A bad battery can display several symptoms.
Here are some common ones:
- Engine cranking is slow: this means the battery has difficulty delivering a charge
- A misshapen battery: it’s bloated, cracked, or leaking
- There’s an odd smell: this can come from leaking battery acid in a lead acid battery
- It’s an old battery: the average battery life is around 3-5 years
If you notice any of these, it’s time to get a new battery.
8. Why Does A Car Battery Drain Out?
Here are some reasons why you might have a dead battery after your engine is off:
- The headlights were left on
- An electrical system (like a cell phone left charging) may be drawing amps
- The battery isn’t being recharged while you’re driving
- The battery is too old and won’t hold a charge anymore
9. How Can I Maximize My Battery Life?
Here are a few methods you can use to increase battery capacity:
- Keep the battery clean: Corrosion buildup can drastically decrease the life of a lead acid battery.
- Check electrolyte level: Remove the vent plugs and ensure that the electrolyte level covers the lead battery plates in all six cells.
- Recharge your battery every three months: Recharging with the appropriate car battery charger can maintain peak battery performance for longer periods of time.
10. What Is An Easy Solution To Car Battery Maintenance?
If you need more than a car battery voltage test, a professional mechanic is your best option. They can handle all the car battery maintenance tasks — including load testing, checking battery cables, and weak battery replacement.
It’s even better if they’re a mobile mechanic and can come to you.
AutoNation Mobile Service is a convenient mobile vehicle maintenance and repair solution.
Here’s why we’re a great option:
- Car battery maintenance and fixes can be made right in your driveway
- Expert technicians execute inspection and servicing
- Online booking is convenient, and service hours are flexible
- Competitive, upfront pricing
- All maintenance and fixes are conducted with high-quality tools and replacement parts
- AutoNation Mobile Service offers a 12-month | 12,000-mile warranty for all repairs
Fill out this online form for an accurate cost estimate for your weak, damaged, or dead battery repairs and maintenance.
Batteries lose their ability to hold a charge as they age and eventually won’t be able to charge up to 100%. Measuring your car battery voltage is an easy way to check your battery’s condition to give you a heads-up if you have a weak battery.
And if your low voltage battery needs some detailed maintenance work, you can always rely on AutoNation Mobile Service.
Contact us during service hours, and our expert technicians will be at your driveway in no time, ready to solve any issues!