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Summary
  • Battery drop testing, or voltage drop testing, is a procedure done to find out if the battery cables and connections are okay.
  • Follow the steps in this article to properly perform a battery drop test. You should perform a voltage drop test if the engine is cranking low or isn’t cranking at all.
  • Voltage drop occurs when the electrical current flows through resistance. Voltage drop tests are more accurate than an ohmmeter in measuring resistance, and they can detect electrical faults that affect the battery or voltages in general.

Regular maintenance is necessary to keep your vehicle healthy and in tip-top shape. Owners that neglect its importance often face hefty repair bills and a sputtering car. However, there are cases when the typical checkup isn’t enough.

Your vehicle is made up of an intricate and complex wiring system that transfers information and power throughout its components. This system is the brain of your vehicle, and there are times when it gets hampered due to a faulty circuit failing to transmit signals within the framework. This is where procedures such as the battery or voltage drop test come in.

What is a Battery Drop Test?

Young,Mechanic,Checking,The,Voltage,Of,A,Battery,Using,A
Before you perform the procedure, you’ll need a voltmeter to check if there is current flowing through the cable.

Battery drop testing, or voltage drop testing, is a procedure done to find out if the battery cables and connections are okay. In some cases, you can also use it to locate excessive resistance in the starting or charging circuit.

Voltage drop testing is essentially done to assess voltage losses at different components of the vehicle, such as the battery, alternator, and starter.

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How to Perform a Battery Drop Test

Before you perform the procedure, you’ll need a voltmeter to check if there is current flowing through the cable.

If you want to measure the difference in voltage (voltage drop) expect the mechanics to perform the following steps to test the starting circuit:

  • Step 1: Connect one of the voltmeter’s leads to the starter motor battery terminal, while the other end is connected to the positive battery terminal.
  • Step 2: The engine is started and the voltmeter’s reading is observed. The ideal result should be less than 0.20 volt (200 mV).
  • Step 3: Test the voltage drop across the “B” and “M” terminals of the starter solenoid with the engine cranking. Similar to the previous step, the reading should be less than 0.20 volt (200 mV).
  • Step 4: Lastly, the voltage drop test is repeated on the ground side of the cranking circuit. Connect a voltmeter lead to the negative battery terminal and another to the starter housing. Start the engine and observe the voltmeter’s reading. The drop should be less than 0.2 volts (200 mV).

Note: The mechanics won’t disconnect the high-voltage ignition wires unless they’re connected to the ground. The high voltage that could occur can cause the ignition coil to fail.

They can also measure the voltage drop of the insulated (power-side) charging circuit. The steps for that variation of the test are as follows:

  • Step 1: The engine is started and runs at about 2000 RPM.
  • Step 2: The headlights are turned on to ensure an electrical load on the charging system.
  • Step 3: The voltmeter is used to set read DC volts, then the positive test lead (read) is connected to the output terminal of the alternator.
  • Step 4: Lastly, the negative test lead (black) is attached to the positive post of the battery.
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The results are then interpreted as follows:

  • A 0.4 volt (400 mV) reading means all the wiring and connections are satisfactory.
  • Anything higher than 0.4 volts indicates excessive resistance between the alternator output terminal and the positive terminal of the battery.
  • Battery voltage means there is an open circuit between the battery and the alternator output terminal.

Significance of Voltage Drop Tests

The significance of the voltage drop test isn’t solely due to the readings and results. It’s also used because it’s more accurate than an ohmmeter in measuring resistance and can detect electrical faults that affect the battery or voltages in general.

More Accurate Than an Ohmmeter

A voltage drop test can better determine the resistance in two components compared to using an ohmmeter. One reason is that the test is more dynamic as the current flows through the component. The conductor also increases in temperature, which increases resistance.

The battery drop test evaluates the circuits under normal operating conditions, making it more accurate than an ohmmeter.

Detection of Electrical Faults

Battery or voltage drop testing determines if the battery cables and connections are okay. Depending on the results, you can find out if there are any electrical faults and easily trace them back to the source.

When to Perform a Battery Drop Test

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You should perform a voltage drop test if the engine isn’t cranking, as the issue can stem from a voltage drop.

You should perform a voltage drop test if the engine is cranking low or isn’t cranking at all, as the issue can stem from a voltage drop. While this is not always the case, the test can help identify and diagnose electrical problems.

What Is a Voltage Drop?

Voltage drop occurs when the electrical current flows through resistance. To be precise, it’s the difference between the voltage at the source and at the electrical device to which it flows. The higher the drop, the greater the resistance in the circuit.

Final Thoughts

The battery drop test lets you test the connections of the internal wiring system within your vehicle. Its importance cannot be stated enough, as it gives you an idea if there are any faults within the system. And if there are any, you can easily trace it back to its source.

See also  Bad Starter Solenoid Symptoms

And while it may seem easy to perform, a battery drop test should be left to professionals, as any misstep in the procedure may affect the reading. So, if you’re having trouble cranking your engine, a battery or voltage drop test may be the answer.

Where to Get a Voltmeter for Your Vehicle

You can’t perform a battery drop test without a voltmeter. And besides that, it’s always useful to have one in case you need it to check other components, such as the motor or an electric panel. If you’re having a hard time finding one in your auto shops, CarParts.com has a wide variety of voltmeters for you to choose from.

Besides the easy-to-navigate website, one thing we can guarantee is the speed and efficiency with which we deliver orders. All our voltmeters are on hand and ready to ship from a warehouse near you, so you can expect your order in as fast as two business days.

You also don’t need to go over budget to get a top-notch voltmeter. We offer our voltmeters at competitive prices to give you the best value for your money. If you have any questions, our friendly customer service team is available 24/7 to assist you.

Check out our catalog, and order your new voltmeter today!

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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