Knowing your battery’s 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 Check The 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 (V) rechargeable battery.
The resting voltage (when the engine is off) measures around 12.6V.
When the engine is running, the battery’s 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 12 Volt car battery, the state of charge is:
- 75% at 12.4V
- 50% at 12.2V
- 25% at 12.0V
- Considered fully discharged at 11.9V
Note: If you’re curious as to whether 8x 1.5V AA batteries are the same as one 12V 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
Follow these 6 simple steps to measure the battery voltage:
- Turn Off The Ignition
- Setup 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 battery terminals for corrosion as it can lower voltage readings (check out our guide to cleaning corrosion here)
- Check the battery for leakage, bloating, or damage — don’t work on the battery if it’s damaged
- Don’t smoke around batteries, as sparks can trigger an explosion
- Wear safety glasses and gloves 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 ignition is off.
To help remove surface charge, you can turn on the headlights for 2 minutes. Ensure the headlights are switched off before you test the vehicle battery.
2. Setup The Tester To Measure DC
Set your voltmeter or multimeter setting to test DC or DCV (for 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 terminal 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 battery positive 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 battery voltage reading is less than 12.4V, it doesn’t necessarily mean you have a bad battery. Some electrical system might have drained it, or your alternator has trouble charging.
Recharge the weak battery and test it again later to see if it holds the charge.
If the battery 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.
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 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?
Is there a way to check it too?
How To Check The Alternator
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 drops 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 between two points in an electric circuit.
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).
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, of 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 a battery charger 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 battery under load and is a more accurate battery health indicator than voltage measurement.
During this test, the battery should be fully charged and is loaded with one-half of its cold cranking amps (CCA) rating at 70°F (or more).
A good battery will be able to maintain 9.6V for 15 seconds with this load.
7. How Do I Know 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 lifespan 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 accessory (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. What 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 to battery replacement.
It’s even better if they’re a mobile mechanic and can come to you.
RepairSmith is a convenient mobile vehicle maintenance and repair solution.
Here’s why they’re a great option:
- Car battery maintenance and fixes can be made right in your driveway
- Expert, ASE-certified technicians execute inspection and servicing
- Online booking is convenient and easy
- Competitive, upfront pricing
- All maintenance and fixes are conducted with high-quality tools and replacement parts
- RepairSmith offers a 12-month | 12,000-mile warranty for all repairs
Fill this online form for an accurate cost estimate for your 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 your vehicle battery is deteriorating.
And if your battery needs some detailed maintenance work, you can always rely on RepairSmith. Contact them, and their ASE-certified technicians will be at your driveway in no time, ready to solve any issues!