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How to test car battery with digital multimeter?

By shafiq usama

TEST CAR BATTERY WITH MULTIMETER

As an electrical engineer, I love explaining how things like circuits and electronics work. I write on my blog to share simple explanations, reviews, and useful tips about the latest technology.

Testing any electrical circuit required good troubleshooting skills and testing equipment. An electrician usually faces two electrical power sources, AC and DC. Testing AC appliances is not much tricky because you don’t have to be conscious about positive and negative probes. But if you don't know how to test car battery with digital multimeter then this guide is for you.

Automotive electricians have to be more careful because a minor mistake can lead to a serious accident. So, first of all let's have a look on how  digital multimeter works.

What is a digital multimeter and what does it do?

"DMM, Digital multimeter or just meter" is a measuring device that measures voltage, current, and resistance using an input connector such as a banana plug. DMM is the basic tool for acquiring measurement data in industrial electronics and maintenance.

How does it work?

The most important part of the procedure is to unplug the device from the power before starting any test. Now you have an easy approach to circuit board and connectors. To help you read DMM, it uses color codes on the test leads. Red is for positive voltage; black is for ground or negative voltage. After this you just have to set the dial on your desired measuring electrical quality. Auto-ranging feature is available in all good quality multimeters. But you can also select the ranges of voltage or current manually. If you want to test ECU of your car then I have made a separate guide on it.

How do you read digital multimeter?

Basically, DMM shows numbers on the screen. If your meter is on AC volts mode it will start to count up with increasing voltage at the input. Digital multimeters have around 16 different modes, use CAL switch to adjust which mode you are using.  When you connect the positive and negative test leads on source the display shows the value.

How to test car battery with digital multimeter?

Testing the voltage of your car battery using DMM

To test car battery with digital multimeter you need to turn off all electrical items in the car. It's very important because if any of them are working, it will show voltage that is not real. Use red probe for positive (+) and black probe for negative (-). If the DMM shows 12 volts then it means that your car battery is fully charged. If your battery voltage drops under 10 volts then you need to recharge or replace the battery. You can also use a battery load tester to properly analyze your car battery.

Testing the current of your car battery using DMM

You can also test car battery with digital multimeter using an ammeter. For this purpose, you have to check the current is in the normal ranges. Almost every battery comes with its standard current rating name plate embossed on it. Most preferably you should use a clamp meter. For this specific purpose I have also made a list of best clamp meters for electricians.

 If you don't have an ammeter, use a multimeter in Amp mode (A) to measure the current. Connect red probe for positive (+) and black probe for negative (-). To check whether your alternator is working properly or not. You need to connect one end of the positive probe to the alternator post and another end of the positive probe to the battery post. If your ammeter shows more than 12 amps then there is a problem with your alternator. Because high amperes mean there is a short circuit in wiring. If you’re still confused then you need to check voltage regulator or other wiring problems in your car. For people who're confused about checking battery amps I have made a separate guide.

Checking if there are any short circuit in your car's electrical system

Use a multimeter in Ohms mode (R) to measure resistance. Set your digital multimeter to the lowest ohms range first. After setting the range you can easily find an open circuit in your car's electrical system. If you find low resistance between two points on your car, that means there is a short circuit and bad wiring under the hood. There might some losing in connection. To cope up such electrical issues, you have to tighten all battery connections. Short circuits causes fuses to blow so if you want to trace blown fuses in your car click here!

How to test a wire for resistance?

Multimeter can use to check if wire is good or bad. To do that, we need to turn on multimeter and set it to continuity mode. After this touch probes on both ends of the wire and wait for few second. You will hear a beep; it means the continuity is ok. You can also read the results which displays on screen. Good wires will show very low or zero resistance. But if there is no beep or high resistance it means the wires are bad.

How to test car relay with multimeter?

Car relay testing is a bit lengthy process. If you want to test car relay with multimeter then i have write a complete method of about testing car relays.

How to test car fuse with DMM?

If you test car battery with digital multimeter and finds everything good. You can use a multimeter to test fuses also. Turn off all electrical items in the car, check fuse with DMM using Ohms mode (R). If DMM shows zero resistance between two ends of fuse then it is good otherwise it needs to be replaced or rewired.

how to test battery with digital multimeter

Testing automotive Alternator to see if its charging your battery

To test whether automotive alternator charges the car battery properly, first turn off ignition switch. Next, disconnect one end of positive probe from the battery post and connect that end of positive probe to the alternator post. Connect negative probe to the alternator body where you removed a bolt from it. Now start your car engine and if your ammeter or multimeter shows more than 12 Volts then it means that the alternator is working properly. If not, there are problems with the regulator circuit in your car.

Most common electrical problems with car battery

Car electrical problems can be caused by bad connections, corroded terminals, faulty fuses and bad circuits. Bad connections cause problems like dimming headlights, flashing interior lights and car electrical items not working properly. Corroded terminals can also cause such issues. You should replace bad fuses to fix exterior lights that are not working like interior lights and some dashboard warning lights. If there is any earth fault in your car wiring then it may get fire also. So, take it seriously. One more major issue is that the car will not get started after ignition. To test car battery with digital multimeter can avoid such issues. I have also made a list of 7 best battery testers for automotive technicians. You can also use them for your car wiring troubleshooting.

Remedy after car battery test with digital multimeter

Jumping a car battery is the best way to revive dead or low battery. Follow these steps to charge or jump-start your car's dead battery.

Make sure both car engines are off.

Turn on emergency lights in cars, preferably flashers or headlights, so other drivers can see you.

Connect one end of the red (positive) jumper cable to the positive terminal of the dead battery.

Connect other end of the red (positive) jumper cable to the positive terminal of good battery.

Connect one end of the black (negative) jumper cable to the negative post on the good battery.

Connect other end of the black (negative) jumper cable to a good grounded metal part under the hood on each car.

Start the car with good battery, let it run for a minute or two to rev up the alternator in both cars.

Now start the other car and remove cables in reverse order that you attached them.

You can remove cables one at a time if the dead battery doesn't come around to life immediately, but after a minute or two, remove the black (negative) jumper cable that you attached to a good metal part on dead car.

Remove red (positive) jumper cable from good battery and finally remove the other end of the black (negative) jumper from bad battery's post. You can give it a little rev before cutting it off to get the alternator up to speed.

If the car with bad battery is unable to start, wait a few minutes and try again. Keep trying until it does start, or you run out of time on the jumper cables. If so, call for road service or ask someone with a car running to give you another jump-start.

Final Verdict

All in all, it is important for automotive electricians to have a good quality digital multimeter on hand at any time. If you are looking for an affordable and reliable DMM. I recommend the fluke 116 Multimeter which offers high-performance at a low price point. It has great battery life as well as accuracy that can be trusted easily when testing car batteries or other electrical troubleshooting issues with your vehicle. In my opinion, instead of multimeter, a good quality clamp meter is also a wise choice to test car battery. I have also made a list of best clamp meters for you. So, to test car battery with digital multimeter grab the one, which suits you the most.