You get in the car and turn the ignition but don’t hear the comforting hum of your engine. It won’t start, and the lack of power indicates it’s probably the battery. Sometimes the reason is obvious, such as realizing you left your headlights on all night. But other than searching “how to tell if the car battery is dead,” how do you know if you can jump it or need to replace it?
A cheap tool and a simple test can let you know if your battery is holding a charge. Learn the easy solutions to potential problems that can come with a busted battery.
How many volts should a car battery have?
An excellent healthy car battery should register about 12.6 volts. Due to the way batteries discharge, it’s crucial that you test the battery after it’s been sitting for at least an hour to get what’s called the ‘resting voltage’. Leave the car overnight and test before you start the car in the morning to get an accurate gauge of your battery’s health.
If you’ve recently been for a drive, as long as the charging system is working correctly, the battery is likely to give a higher reading than the resting voltage, and so could be misleading.
Testing a battery with a multimeter is a simple process. The first thing to do is make sure you can access the battery terminals (the metal connections on the top or front of the battery).
Batteries are commonly located in the engine bay to one side of the engine. If the battery is not immediately obvious when you open the hood, consult the owner’s manual. In modern cars, the battery will often have a plastic cover that will unclip, hinge up, or occasionally require removing a few bolts or screws.
There may also be a red cover over the positive (+) terminal that will lift off or snap open too. Once the battery is exposed, be extremely careful that nothing metal touches the terminals and causes a short, so don’t set wrenches or other tools on top of the battery.
Test a Car Battery with a Multimeter
Prepare the Battery
The first step is to locate the vehicle battery (consult the owner’s manual) and determine if there is any dirt or corrosion at the positive and negative terminals. The positive terminal usually wears a red cover and a “plus” sign, while the negative terminal has a black cover and a “minus” sign. Since corrosive buildup can keep the multimeter from taking accurate voltage readings, it should be scrubbed off using fine-grit sandpaper.
Gloves should be worn to prevent skin exposure to harmful chemicals and battery acid. Once the terminals are clean, they will serve as the connection points for the multimeter’s probes.
The multimeter may look complicated due to its various measurement settings, but the general operation is fairly simple. For testing the electrical output from a vehicle battery, the multimeter dial should be turned to the “20 volts” setting. But before the multimeter can be used, all surface charges from the battery must be removed to allow for an accurate reading. To do this, the headlights should be turned on for about two minutes, then turned off.
Measure and Analyze
For measuring battery load, the multimeter has two probes: red and black. The red probe is for contact with the positive terminal, and the black probe is for contact with the negative terminal.
When the probes touch the terminals while the car is off and the battery is resting, the multimeter display should show a reading of 12.2 to 12.6 volts (full charge). This voltage range means the battery is in good condition for starting the vehicle. If the measured reading is less than 12.2 volts, the battery’s resting voltage is weak, which means it most likely needs to be charged or replaced.
Once the resting voltage has been determined, it is time to get a reading on the crank cycle. This is the moment that the vehicle is turned on, and the battery is under the most draw because of the higher amount of energy needed to drive the starter motor. To get this reading, a second person will be needed for starting the ignition.
As soon as the car is turned on, the voltage reading will drop for a quick moment but should not fall below 10 volts. If it falls below 10 volts, it means the battery does not have sufficient turnover strength and is prone to failure. Again, in this case, recharge or replacement of the battery may be necessary.
Immediately following the crank cycle, the vehicle will begin to idle and maintain a steady draw from the battery. With the motor running, the multimeter rating should stay in the 14 to the 14.5-volt range. Dropping below 14 means either the battery is weak and unreliable for sustained vehicle operation, or the alternator is failing.
The alternator’s job is to generate energy to feed the electrical system and charge the battery while the vehicle is running.
To test the alternator, turn on all of the vehicle’s electrical equipment – headlights, interior illumination, climate controls, stereo. This will maximize the voltage load.
If the multimeter reading drops below 13.5 volts, the alternator struggles to charge the battery properly and may need replacement. It is time to consult with a licensed professional for a second opinion.
Utilizing a multimeter can provide a car owner with valuable information about their vehicle’s battery and electrical system. Periodic testing can help predict and prevent imminent failures that often occur without warning.
Symptoms of Low Car Battery Levels
The most obvious sign of a low battery level is slow cranking when attempting to start your vehicle. In worse cases, there may be no cranking at all. If your power window malfunctions or if your heated seats or electronic defrosters are not functioning as they should be, it may also be a sign of a low car battery.
You may also have problems opening your car door and trunk with a low battery level if your vehicle is equipped with remote keyless entry.
Keep in mind that a low or dead battery does not automatically mean that it needs replacement. Several factors may affect your car battery’s state of charge, such as not driving your car for long periods or not driving it long enough.
Also, you may want to check your vehicle’s alternator and the charging system for issues. Aside from a faulty battery, there may be something wrong with your vehicle’s electrical system, causing your battery to drain.