How to Test Car Batteries with a Multimeter? When you follow this step-by-step instruction from the Motor Guider team, testing a car battery with a multimeter is simple. While our various locations specialise in-car information, news, specs and features, we also understand that knowing what to look for when trying to undertake repairs at home may save you a lot of time and money. Here you can find out if it’s time to replace your automobile battery or alternator.
Test Car Batteries with a Multimeter
Every car has a battery because it would go nowhere if it didn’t. And those enrage-inducing moments when you crank the key and hear nothing but a click always happen when you least expect it. We’ll show you how to use a simple multimeter to do a few battery tests so you can figure out what’s wrong.
How to know if car battery needs to be replaced?
The following are the most prevalent symptoms of a malfunctioning battery:
- The dashboard’s battery light was turned on.
- When the engine is first started, it cranks slowly.
- The vehicle needs to be jump-started frequently.
- When you start the engine, it clicks.
- The lighting is faint.
- The car will not start.
What is a Multimeter?
A multimeter reads the voltage in your car battery and tells you how much energy is currently stored in it.
How to Test Car Batteries with a Multimeter?
- Turn on the headlights for two minutes to clear any surface charge from the battery.
- Set the multimeter to a voltage range of 15-20 volts.
- Turn out the lights.
- Connect the positive and negative battery terminals to the multimeter.
- You may have a faulty battery if the voltage isn’t around 12.6 volts.
- Now start the car and look for a voltage reading of above 10.
- When the voltage drops below 5 while the automobile is operating, it is a sign that something is wrong and should be replaced right away.
How many volts should a car battery have?
The voltage of a good automobile battery should be around 12.6 volts. It’s crucial to test the battery after it’s been sitting for at least an hour to determine what’s known as the resting voltage.’ If you’ve been driving recently (and the charging mechanism is working properly), the battery is likely to produce a greater number than the resting voltage, which could be misleading.
Better yet, leave the car overnight and test the battery the next morning to receive a more accurate picture of the charge state.
It’s simple to test a battery with a multimeter. The first step is to ensure that you have access to the battery terminals (the metal connections on the top or front of the battery).
Batteries are usually found on one side of the engine in the engine bay. Consult the owner’s manual if the battery is not visible when you open the hood. In most current cars, the battery is protected by a plastic cover that can unclip, hinge up, or be removed with a few nuts or screws. There may also be a red cover that lifts off or snaps open over the positive (+) terminal.
When the battery is exposed, be sure nothing metal touches the terminals and produces a short, so don’t place wrenches or other tools on top of it.
Also Read: How does a vehicle tracking system work?
How to check your alternator with a multimeter?
An alternator is a device that generates electricity and charges a battery. Not only that, but it also takes over and supplies power to the car’s electrical systems while you’re driving.
So, while the engine is running (and keeping an eye on moving parts), use your multimeter to do the same battery test as before. At regular idle speed, a healthy charging system should read between 13.8V and 14.4V.
Anywhere outside of that range, your car is either undercharging or overcharging, both of which will reduce battery life and necessitate additional study.
How to find dead cells in a car battery?
First and foremost, knowing that a battery cell is dead is useless, much like knowing that the battery won’t hold a 12.6-volt charge because you can’t fix it. As a result, a resting voltage test is equally as good as a diagnosis.
A battery normally does not go bad all at once; instead, portions of the battery’s cells will die. When starting an engine, slow turning over is a sign of dead battery cells.
Most modern automobile batteries are sealed and maintenance-free, however, some older batteries include individual cells that can be accessed. Individual caps or a plastic cover that clamps overall, or several, of the cells will be used. Make sure you don’t acquire any liquid on your skin because the cells contain a mixture of water and sulfuric acid.
A hydrometer-style battery tester that detects the specific gravity of the battery acid is required to test each cell. You can detect if a cell is alive or dead by the number of floating balls.
Pro Tip: Before you detach your battery, make sure you know your stereo’s anti-theft code; if you don’t, it might not operate when you reconnect it!
Also Read: How can I Start My Car with my Phone?