What Color is Positive on a Battery?

If you have to connect your car battery’s cables, which one of the two (red or black) do you connect to the positive terminal?

The positive on a car battery is red, whereas the negative is black. The terminals may or may not be colored, but the red cable is connected to the battery’s positive terminal, and the black cable to its negative terminal.

Terminals of Car Batteries

Battery Terminal Color Coding


Car batteries have two terminals: A positive terminal and a negative terminal.

The positive one is marked ‘+,’ and the negative one is marked ‘-.’ Technically, color doesn’t need to be associated with either terminal, but a standard scheme or convention exists to make it easy to identify and distinguish them.

Under this scheme, red is associated with positive and black with negative. So you’ll typically see a red cable attached to the battery’s positive terminal and a black cable attached to its negative terminal.

The Function of Battery Terminals

Battery terminals have a certain function.

The positive side is called the cathode, and the negative side is the anode. In a lead-acid battery, the cathode is made of lead oxide and the anode of metallic lead. In a lithium-ion battery, the positive electrode is made of a combination of nickel, manganese, and cobalt oxides, and the negative one is made of graphite.

The positive terminal is connected to the electrode where the battery’s electrons leave, and the negative terminal is connected to where its electrons enter. The latter is grounded. Together, they form a circuit when connected to a load in between.

circuit formed by a battery’s terminals
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The terminals must be connected properly for the circuit to be formed and their functions to be served.

Color Coding

positive and negative battery terminals
Color coding helps identify the positive and negative battery terminals

The Importance of Color Coding

Color coding for vehicle batteries is only a convention.

However, it’s important because it helps easily identify and distinguish between two opposite terminals and cables. It’s important to ensure the correct cable is connected to the correct terminal because it’s a DC circuit, so the color coding helps.

If you mistakenly attach the cables to the terminals the wrong way round, it could cause a short circuit, and the battery would deteriorate rapidly.

Which Color First?

When connecting the power cables to the car’s battery, do the red first, then the black.

The red color is for the positive, and the black one is for the negative. So attach the red-colored cable to the battery’s positive terminal first, then attach the black-colored cable to its negative terminal. Also, ensure both cables are attached securely. Tighten the nut with a spanner or wrench.

connecting the positive (red) terminal
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The negative terminal, which you will connect after connecting the positive terminal, is grounded to a metallic part of the vehicle’s chassis.

Different Scenarios

Let’s consider two scenarios to understand better vehicle batteries’ terminals and color coding: faulty connections and unmarked terminals.

Effect of Connecting Wrongly

What would happen if you connected the cables wrongly?

If you don’t connect the red to the battery’s positive and the black to its negative, the vehicle will fail to function normally.

A worse situation would be if the two terminals were mistakenly connected directly. In this case, it would cause a current surge between them. The battery would heat up quickly if the connecting element creating the short circuit is not immediately disconnected.

What if the Terminals are Not Marked?

Now that you know red is positive on a battery and black is negative, what if the terminals are not marked, or the markings are faded? How would you tell which is positive and which is negative?

Vehicle batteries without marked terminals are usually distinguished by size instead. You will notice that one is larger and smaller than the other. Even if the terminals are marked, there might be a size difference. Usually, the difference is in the diameters (not their vertical lengths).

The positive terminal will be the larger one, and the negative one will be the smaller one (with a smaller diameter). So you connect the red to the terminal with a larger diameter and the black one to the other smaller diameter terminal.

Terminal Size Difference


Image and Video References

Color coding helps identify the positive and negative battery terminals: https://www.amazon.com/CZC-AUTO-Terminal-Negative-Connectors/dp/B099JVBPMX?th=1

Indicates what color is positive on a car battery terminal: https://www.amazon.com/CZC-AUTO-Terminal-Negative-Connectors/dp/B099JVBPMX?th=1.

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About Alex Robertson

c3c9d43f1f0d14c4b73cb686f2c81c4e?s=90&d=mm&r=gCertifications: B.M.E.
Education: University Of Denver - Mechanical Engineering
Lives In: Denver Colorado

Hi, I’m Alex! I’m a co-founder, content strategist, and writer and a close friend of our co-owner, Sam Orlovsky. I received my Bachelor of Mechanical Engineering (B.M.E.) degree from Denver, where we studied together. My passion for technical and creative writing has led me to help Sam with this project.

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