A multimeter is the perfect tool to help diagnose many electrical faults. It lets the user know the amount of current flowing from a particular source.
A multimeter is also a great tool to use when diagnosing a faulty car battery. In this short guide, I will explain how to test a car battery with a multimeter. Our Car Battery Overview page is a great resource as well as our Common Signs Of A Bad Car Battery post.
What Is A Multimeter?
A multimeter is a tool that can measure voltage, amps, and resistance between 2 points. Electricians will often use a multimeter to find out if enough current, or any current is passing through a circuit.
You can buy both Analogue Multimeters and Digital Multimeters. Digital multimeters have become extremely accurate and can pick up very slight changes or fluctuations in current.
If you use a multimeter to test a car battery, the readings that you will need do not have to be highly accurate, but if you are a hands-on person, once you learn to use a multimeter on a car battery, you will find many other uses for it.
To use a multimeter on a car battery, you just set it to the type of reading that you want and place the 2 leads or prongs on the separate terminals of the battery that you are testing. The current that is flowing between the 2 points will register on the multimeter display.
Where To Buy A Multimeter
Learning how to use a multimeter to test a car battery is easy and once you have done it, you will likely do it again and again throughout your lifetime. This is a good reason in itself to own a multimeter, but if you do not own a multimeter, you could first check with family or friends if they own one.
A multimeter good enough for testing a car battery is generally not very expensive, so if you are thinking about buying one and would like to know where to buy a multimeter, you can read our Best Multimeters buyers guide.
I have also included the multimeter that I use below. It is a little more fancy than what you may need but I do find them very useful and get quite a bit of use out of it.
KAIWEETS Digital Multimeter TRMS 6000
How To Test A Car Battery With A Multimeter
A car battery that keeps going flat for no apparent reason could be old, worn out, or just faulty. A fault may also lie with your car. The alternator in your vehicle should provide a regular top-up (maintenance) charge to the battery each time you start and drive your car.
So how can you tell if the fault is with your car battery or the alternator? If you follow this guide and learn how to test a car battery with a multimeter, then you will understand how to diagnose where the fault may lie.
There is nothing worse than spending money on an expensive car battery to find out that your car battery was not at faulty at all, and learning how to test a car battery is one of the best ways to avoid this costly mistake.
Before you test your car battery, you need to first check that you have a maintenance free car battery.
You can tell a maintenance free car battery as they usually have a Charge Dot on the top, which will change color depending on the battery’s condition. A green dot will indicate good health and charge; no dot will show a charge is needed, and a yellow dot would indicate a faulty or flat battery.
Another way to identify a maintenance free car battery is to check if it is completely sealed or whether there are removable caps along the top of the battery. This is where fluid can be added when it becomes low. Maintenance free batteries are usually completely sealed and water cannot be added which is why they are maintenance free.
If you do have a maintenance free battery, you will instead need to test it with a hydrometer.
If you have recently charged your battery, you will need to remove the surface charge before you can test the battery, otherwise you may get a false reading. Turn your car over a few times, or just leave the battery to sit for a few hours after charging. A faulty battery may still hold a small charge which will deplete quickly once used.
How to test a car battery with a multimeter:
- First, locate your car battery.
- Plug the leads into your multimeter – Red is (+) positive, and black is (-) negative or ground.
- Make sure that your car engine is switched off.
- Set your multimeter to receive the correct reading (20 DC Volts).
- Place the positive (+) Red prong to the positive battery terminal and the negative (-) Black prong to the negative battery terminal.
- Ask somebody to turn on the headlights to apply a light load to the battery.
- Check the reading on your multimeter.
The voltage of a car battery can vary but you will be looking for a reading similar to those listed below:-
If you get a reading of 12.5 volts or higher, then your battery has a good charge.
A reading of around 12.3 Volts suggests approximately 75% battery charge.
A reading of 11.8 Volts or less can indicate a battery of 25% charge or less.
The voltage of a car battery can display as slightly high in warm very warm weather or slightly lower in extreme cold, so keep this in mind.
If the reading you receive through your multimeter is low, you need to charge your battery and test it again. If the reading does not improve, you may want to replace your battery.
Hopefully you have learned successfully how to test a car battery with a multimeter, and if you are lucky, you do not have a faulty car battery.
If you do have a faulty or worn out battery, there is another option to replacing it. If you have ever though of buying a used, reconditioned car battery, you will be pleased to know that reconditioning of batteries is pretty easy to do and can save you loads of $$, especially over your lifetime.
Thousands of people have had great success and saved a lot of money using a system called the EZ Battery Reconditioning System. I have enjoyed learning to recondition batteries through using this system and have written a review of the system here.
The system teaches in easy to follow step by step instructions that are designed for anyone, even if you have no prior technical experience. It teaches how you can recondition almost any type of battery not just car batteries.
Below is a short video detailing what the EZ Battery Reconditioning System can do.