Is your car battery on its last legs?
Knowing your car battery voltage can be valuable in extending its life and avoiding unexpected breakdowns.
But what’s the magic number?
We’ll explore the ideal car battery voltage, show you how to test the battery voltage (with and without a tester), and more.
Let’s go.
This Article Contains:
- What Should My Car Battery Voltage Be?
- How to Measure Car Battery Voltage
- How to Check the Car Battery Without a Tester
- How to Check the Alternator
- 9 FAQs about Car Battery Voltage
What Should My Car Battery Voltage Be?
The standard automotive battery is a 12 volt battery.
The normal car battery voltage, measured when the engine is off, should read 12.6 volts (known as resting voltage). Car batteries usually provide these 12.6 volts through six cells, each supplying around 2.1V.
When the engine is running, the alternator takes over the task of supplying power and recharging the battery. In this case, the battery’s voltage should fall between 13.5V and 14.5V. Anything significantly above this range could be excessive voltage.
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:
- 70% at 12.32 volts
- 50% at 12.06 volts
- 20% at 11.58 volts
- Considered fully discharged at 10.5 minimum voltage.
Next, let’s look at a simple test that can help your car battery keep functioning properly.
How to Measure Car Battery Voltage
To check your car’s battery condition, you’ll need a battery tester, like a voltmeter or multimeter.
The multimeter has two probes for measuring the battery voltage and load: red and black. The red probe is for contact on the positive terminal, and the black probe is for the negative terminal.
Here’s a quick rundown of the steps to measure the battery voltage:
- Turn off the ignition
- Set up the tester to measure DC volts
- Touch the probes to each battery terminal
- Check voltage with the engine off
- Do a crank cycle test
- Measure voltage with the engine on
But before you begin your battery test, you must follow specific safety measures.
Safety Measures
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. Be sure to clean off any corrosion before starting the test.
- 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.
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.
Now, let’s check out the battery test steps in detail.
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. Turn off the headlights before testing the battery capacity.
2. Set Up the Tester to Measure DC Volts
Set your voltmeter or multimeter setting to test DC voltage (Direct Current Voltage).
If there’s a DC voltage range, set the voltage range higher than the voltage you’re testing. Since it’s a 12V car battery, set the multimeter to 20V.
3. Touch the Probes to Each Battery Terminal
Locate the positive terminal (+) and 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, you may have swapped the probes, and you need to switch the battery post they’re touching.
4. Check Voltage with the Engine Off
Healthy car batteries should have a resting voltage of 12.6V.
If the battery’s voltage is less than 12.4 volts, it doesn’t necessarily mean you have a bad lead-acid battery, just low voltage. Some electrical components might have drained it, or your alternator has trouble charging.
If the reading is low, it’ll need recharging. It’s best to do this with a battery charger. Bear in mind that a trickle charger will prevent the battery from charging too quickly, but it can take days for a fully charged car battery.
After recharging, test the battery again to see if it holds the charge.
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.
Have a friend 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, the battery doesn’t have enough turnover strength, and you’ll likely need a new battery.
6. Measure Voltage with the 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 13.5-14.5V. If the voltage reading is significantly lower or higher, it could mean issues with the alternator or battery.
But what if you don’t have a volt meter?
Can you still check your battery condition?
How to Check the 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?
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, the alternator has trouble charging the car battery, and you should have a mechanic look at it.
B. Without a Tester
If you don’t have a tester handy, you can still test the alternator.
Ensure the car is in “Park” and the parking brake is engaged 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.
We’ve covered how to check the alternator, which is important in maintaining your car battery voltage. Now, let’s clear some related doubts.
9 FAQs about Car Battery Voltage
Here are answers to some common car battery queries:
1. What’s a Voltmeter?
The voltmeter 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, meaning driving faster will generate 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. 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 12.4 volts.
A reading below 12.2V suggests your battery is partially discharged, and you could use a battery charger.
6. What’s a Car Battery Load Test?
The battery load test helps assess the 12-volt battery under load and is a more accurate battery health indicator than voltage measurement. A load test directly measures the voltage a fully charged battery generates when placed under load.
During this test, a fully charged battery is loaded with half 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 batter can 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: 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:
- You left the headlights on
- An electrical system (like a cell phone left charging) may be drawing amps
- The battery isn’t recharging 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.
Ensure Smooth Starts with AutoNation Mobile Service
As the electrical components within batteries age, they lose their ability to hold a charge and eventually lose power. Measuring your car battery voltage is an easy way to check your battery’s condition.
And if it turns out you do have a weak battery, give AutoNation Mobile Service a call. We’ll replace your weak battery directly from your driveway. We also offer a 12-month, 12,000-mile repair warranty.
Contact us to solve your battery issues today.