How to Test a Car Battery Yourself
Are your dashboard and lights turning on, but the car won't start?
Do you hear a click or the dash lights dim when you try to start the car?
If you are noticing any of these symptoms, you may have a bad battery.
Before you replace that expensive battery, it is good to perform a battery check to ensure the battery is bad. Otherwise, you may be replacing a good battery for no reason.
How to test a car battery with a multimeter or voltmeter?
Testing a car battery is simple and requires that you have a digital multimeter. Don't worry if you have never used a multimeter before; it's straightforward.
In short, what you will need to do is set the multimeter to the 20 volt DC setting. Next, turn off the ignition and lights. Connect the red cable to the positive (+) terminal on the battery and the black cable to the battery's negative (-) terminal.
- Turn off ignition To test the car battery with a multimeter; you need to have the engine turned off.
- Locate the car battery. The first step to check a car battery is to locate the battery. In most cases, the car battery is in the engine bay. Open and look for the battery near the engine. If you have a European car or a high-end luxury vehicle, the battery is more likely to be in the trunk. Some models may have the battery under the passenger seat or the rear seat cushion. Can't locate car battery? If the car battery is hidden under the seat or is mounted in a difficult to reach area, you can use the jump-starting terminals to connect your multimeter. You may notice a 0.0 to 0.2 voltage difference between the battery and jumping posts.
- Set up your multimeter to a 20-volt setting. Set your multimeter to measure voltage. Most multimeters have two voltage settings. One is Direct Current (DC) and has a straight line on top of the V symbol. The other is Alternative Current (AC) and has a ~ on top of the V. The ~ symbol represents a sine wave.
- Car batteries produce Direct Current, so make sure to set your voltmeter to V with a dash (-) line on top. Plug your cables into the two ports of your voltmeter. These are called test leads in technical terms.
- Your multimeter's red cable or lead should be plugged into the + port and connected to your car battery's positive terminal.
- Connect Negative. The black cable should connect to the - port ( Neg, Ground) on your digital multimeter and the negative terminal on your car battery.
- Measure Voltage Once you turn the multimeter on and set the voltage range properly, the multimeter will show the battery's voltage.
Determine battery status
Determine if your battery is charged or not.
Battery Voltage Guideline
|Engine Running: 13.7 to 14.7 volt||GOOD|
|Engine Off||Charge Status|
|12.6 or more volts||100% Charged - GOOD|
|12.4+ Volt||75% Charged - GOOD|
|12.2 - 12.4 Volt||50% Charged - Needs Charge|
|12.05 Volt||25% Charged - Needs Charge|
|Under 12 volt||Battery Discharged|
Just because the battery is reading over 12.6 volts doesn't always mean the battery is good. The battery may read over 12.4 volts yet not output enough Cold Cranking Amps (CCA) to start the car. In the next section, you will learn how to perform a battery load test.
How to find out if my car battery is good?
Any automotive repair shop or even some auto parts stores can load test a battery for you.
It is not accurate to assume that because a battery is discharged, the battery itself is bad. To determine if the battery is good or not, charge up the battery and perform a load test.
During a load test, a car battery needs to supply at least 9.5 volts during engine cranking. The battery needs to be fully charged to perform a load test accurately.
Checking the voltage can be misleading because the battery may test well based on voltage but can not hold a load.
In modern vehicles, a load test is a better way to tell if your battery is good or needs to be replaced.
- Connect the multimeter probes to the car battery.
- Set voltmeter reading to auto-detect or 20 volts.
- Note battery voltage with the engine off.
- Crank up the car and, in the meantime, have a friend watch the voltage drop on the multimeter. (It is ok if the car doesn't start.)
- If the voltage drops less than two volts, for example, from 12.5 volts to 10.5 volts during cranking, the battery is good.
- If the voltage drops more than two volts or goes under 9.5 volt during cranking, the battery needs to be replaced soon.
How to check a car battery with a test tool?
The easiest way to test a car battery is to use a battery analyzer or an electronic or conductance tester.
An electronic tester sends an alternating frequency signal through the battery to determine the condition of the cells. In an old battery, the internal plates of the battery may have low current flow and conductivity.
In other words, an electronic tester measures the conductance of the battery cell.
Some but not all battery analyzers measure the Cold Cranking Amps (CCA) of the battery, such as the Foxwell BT-705 Battery Analyzer.
By measuring the CCA capacity of the battery, you can determine the remaining life of the battery.
How to charge a dead car battery?
Many car owners jump-start the car and let the alternator charge the battery.
While letting the alternator charge the battery works, in most cases, it is not the best method to charge a car battery and can shorten its life.
Your car's alternator is designed to supply voltage to run your car and not charge a dead battery. Here are two reasons why you should not charge a car battery using your alternator.
If the battery is fully discharged and you jump-start the car, you risk causing an electrical problem, triggering Undervoltage fault codes on your vehicle's control modules, and even have the car go into limp mode.
As would be when the alternator charges the battery is not healthy for the battery, a fast charge would be the case. If you want to charge your battery to 100% properly, use the slow charging method.
A trickle charger takes longer but brings the battery to a fully charged state.
To properly charge a car battery, you don't need to remove it from the car. Even though removing or disconnecting would be the preferred method.
- Get any 12-volt Trickle Charger.
- Connect the red positive clamp to the battery positive terminal.
- Connect the negative clamp to the negative battery terminal. Note: Many vehicles have battery jump-starting terminals under the hood. In most cases, car manufacturers recommend that you use the jump terminals to charge the battery.
A battery that shows low voltage may still be a good battery if it is fully charged. You need to check if the battery will hold a charge to determine if it is good or bad.
To determine if the battery is defective, follow the next section's procedure to perform a battery load test.
What are the symptoms of a bad car battery?
If your car battery doesn't hold a charge or keep discharging when parked, the battery itself could be the culprit.
Obviously, the battery is bad in most cases, but sometimes battery issues are not as obvious.
- Battery light on
- Car won't start
- Click, click, click when trying to start the car.
- Engine cranks slowly
- The battery doesn't hold a charge
Frequently Asked Questions
How many volts should a car battery have?
A good car battery should read 12.5 volts or higher. If your car has been sitting for a long time, there is a good chance the battery will read below that. Don't assume the battery is defective. Please charge the battery ideally using a trickle charger to bring it up to 100% charged status.
My car battery keeps on dying?,
If your car battery keeps on during when the car is parked the problem may not always be a bad battery. Some cars develop what is called a parasitic discharge. This means one of the car systems is still using the battery even when the car is turned off. It will be the same as if you left the light on. Other systems that can cause parasitic draws include amplifiers, aftermarket stereos, electronics plugged into the 12-volt outlet that is always powered on, power seats, defective ECU control unit, to name a few.
Can I drive the car to charge the battery?
In theory, yes, you can drive the car to charge the battery. Ideally, you want to avoid charging a car battery via the alternator. Alternators are designed to produce electricity to run the car and not change a fully discharged battery. Charging a car battery by the alternator becomes even more of an issue on modern luxury vehicles. The low battery voltage often triggers electrical warnings such as airbag light on or transmission goes into limp mode.
How can I test a 6 volt or 24-volt motorcycle or boat battery?
This procedure shows you how to test a 12-volt battery with a multimeter. Test other battery sizes such as 6 volts or 24 volts using the same procedure, but make sure to select the appropriate voltage range on your multimeter or set it to auto-detect.
How long do car batteries last?
Most car batteries last about four to five years. It is not uncommon for a car battery to fail after two years or last over seven or eight years.
Published on: Tuesday, December 10, 2019.