How to Check a Battery Drain with a Multimeter

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Battery drain occurs typically when there is continuous emancipation of energy when you switch on your engine, and this usually emerges due to an occurrence of a short circuit. However, a severe battery drain can also be caused by a faulty battery or an alternator diode, so it is wise always to scrutinize these two. Typically, depending on the energy being emitted, a parasitic draw sucks all the juice from your battery in a little time.

Therefore, in this article, you will be taken through how to check a battery drain with a multimeter and be in a better position to identify what exactly could be the issue. Here are some of the steps you need to follow to determine this best. 

Preparation for the test

You should first confirm that your battery is fully charged before you start on any test, with the voltage needed to be around 12.6V. Consequently, switch off all your machine’s accessories and remove your key from the ignition switch and then disconnect the device from the power source even if your machine is switched off.

Additionally, in case your vehicle features a fuse box below the dashboard on the driver’s side, make sure you open the driver’s door and using a clamp press hold the switch of the door while leaving the door opened. The purpose of the clamp is to keep your dome light off as you run your tests and do the same procedure on the passenger side if it has a fuse box.

It is also vital for you to locate the fuses for your car computer, stereo as well as your dash lock since this will enable you to know whether the circuits show any energy presence as you conduct the test.

To know more about what fuse protects in the circuit, check your manufacturer’s manual and if you do not have one consult with your experts or buy one from the repair shop. Once you are done with these preparations, you are now ready to take start checking for battery drain. 

The amperage battery drain text

This test is very crucial when it comes to older vehicle models which usually come well-armed with one or more computer modules. To commence on amperage battery drain test, you need to disconnect the negative battery cable from the battery terminal, and after that, connect your digital multimeter probe also to the negative battery post. Moreover, connect the meter’s positive to the battery from the cable terminal you ran a disconnection on.

After that turn on your multimeter and set it on the highest settings on the DC and check what it displays. Ideally, it should read zero amps and after that dial the lower setting on your amperage scale until you detect the flowing current.

If your vehicle does not have a parasitic battery drain its current ranges approximately 50 milliamps, but if it has an issue, the current will be higher than the required range.

Now for you to locate a faulty circuit, you will have to remove fuses out one by one until you recognize an abnormal amperage reading varying from the normal range, meaning that the circuit protected by the fuse is faulty. Once you locate the circuit, check your user manual to examine the wiring chart for the circuit. By doing this, you will be able to know the prospective trouble point and be better placed to troubleshoot the problem correctly. 

The voltage-drop battery drain test

This test allows you to examine whether there is any voltage drop in your vehicle’s battery. It would be best if you referred to your manual to have an idea of the duration that your car modules need to be switched off, and then check whether the control modules have a cycle that is either on or off.

Doing this allows you to read a voltage drop on these particular modules when your car is turned off. Consequently, set your digital multimeter to the millivolts and the turn it on.

First, you need to test for a voltage-drop drain on the fuse of your computer’s circuit and dashboard clock which usually has undergone minimal energy loss. On the back of the fuse touch one of the test points using your meter’s leads and the other fuse with the other lead and observe what is displayed on your multimeter.

Usually, circuits that have entirely no current flowing through it read a voltage drop of 0.0 Mv. Anytime you identify a voltage drop, and you need to know you have found a circuit that has battery drain.

Bad alternator diode test

A diode helps you to convert alternate current(AC) generated by the alternator into a direct current (DC), hence allowing electricity travel one way to your battery as well as to other electrical systems. As it does this, it also blocks current from flowing in the opposite direction from the battery to the alternator.

Whenever diodes fail, this prevents the flow of continuous electrical supply to the electrical systems. Therefore, to inspect for a defective alternator diode, switch on your multimeter to its lower setting on the alternating current voltage scale.

Car battery hydrometer test

It is the quickest and easiest way to examine the state of charge as well as the battery’s health, thereby know whether or not the battery needs replacement. When running this test ensure you set your multimeter correctly, and any reading below the 1.265 mark is usually a sign that your car battery needs to charged. Nevertheless, if the difference between the more cells readings ranges between 25 to 50 points, then this is a sign of battery drain. 


If you are looking to learn how to check for battery drain using a multimeter, reading through this article has provided you with all the valuable information you need. Therefore, whereas it might occasionally seem challenging to examine for battery drain with a multimeter as it is often time-consuming, doing this is very important. Consequently, you will be able to better make use of your car and avoid any unforeseen issue while you are out on the road, thereby guaranteeing your safety.

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