Checking a car battery is a simple procedure you can perform yourself.
If your car battery doesn't hold a charge or keep discharging when it is parked, the battery itself could be the culprit.
In most cases, it is obvious that the battery is bad, but sometimes battery issues are not as obvious.
In this guide, we will show you how to check the battery voltage with a digital multimeter to determine if the battery is good.
To test the car battery with a multimeter you need to have the engine turned off.
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 under 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 the 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 your multimeter to measure voltage. Most multimeters have two voltage setting. 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 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 term.
The red cable or lead of your multimeter should be plugged into the + port and connected to the positive terminal on your car battery.
The black cable should connect to the - port ( Neg, Ground) on your digital multimeter and also the negative terminal on your car battery.
Some multimeters have an auto-range but in others, you may need to set the dial to 20 volts to get an accurate reading.
Determine if your battery is charged or not.
|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.
Any automotive repair shop or even some auto parts stores are able to 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 accurately perform a load test.
Checking the voltage can be misleading because the battery may test good 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.
The easiest way to test a car battery is to use a battery analyzer or also known as 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.
Many car owners simply 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.
The alternator in your car 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 vehicles control modules and even have the car go into limp mode.
A fast charge as would be the case when the alternator charges the battery is not healthy for the battery. If you want to properly charge your battery to 100% use slow charging method.
A trickle charger takes longer but brings the battery to fully charged state.
To properly charge a car battery you don't need to remove it from the car. Even though removing or disconnecting it would be the preferred method.
A battery that shows low voltage may still be a good battery is 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 procedure in the next section to perform a battery load test.
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. Charge the battery ideally using a trickle charger to bring it up to 100% charged status.
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. Which means one of the systems in the car 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.
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 warning such as airbag light on or transmission goes into limp mode.
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.
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.