How To Disconnect A Car Battery (2023 Guide)

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Reviewed By: Charles Noyes

If mitochondria are the powerhouse of the cell, a car battery could be called the powerhouse of the engine. A charged battery is needed to start the car engine, but when it's time for a replacement, it's important to know how to disconnect a car battery.

Luckily, disconnecting a car battery is relatively simple when you have the right tools and basic electrical knowledge. The main objective is to stay safe while working with any active current and disconnecting battery terminals in the correct sequence, both of which we will go over in detail.

Disclaimer: Working with car batteries poses risks such as electric shock and potential damage to vehicle systems if improperly handled. Please use caution while attempting any vehicle maintenance and always consult your car manufacturer's manual.

There are a few circumstances where you should disconnect a car battery:

Car batteries work by converting a chemical reaction into an electric current. Inside every battery are an anode (often lead or carbon), a cathode (lead oxide or lithium oxide), and an electrolyte (sulphuric acid or lithium salt). The electrolyte acts as a catalyst for the anodes and cathodes to produce electrons, which create electricity. That electricity is then transferred from the battery terminals to the engine and other parts of the vehicle.

It is worth noting that this process also works in reverse order, which is why you can use a battery charger to revive a dead battery.

There are several ways to measure your car battery to see if it is still good for use. Most car batteries last between three to five years, though neglect from a car owner can necessitate a faster battery replacement.

Here are some ways to determine if you need a new battery:

Another way to check your battery's charge is via an automotive multimeter. A multimeter is a handheld device that can read electric currents, voltages, and several other measurements of electricity.

To assess your car battery's health with a multimeter, set it to 20.0 DC volts and touch the negative and positive probes to the appropriate battery terminal. If fully charged, the battery should read approximately 12.6 V. If the vehicle is running or was recently driven, you can expect a higher reading because it will still have an excess charge.

If you don't have a multimeter, you can typically have your car battery assessed at an auto parts store.

While disconnecting a car battery, you may want to use gloves and safety goggles as a precaution. Even with fading power, the old battery may still have enough residual charge to cause a shock if someone touches both terminals simultaneously.

Motorcycle batteries are similar in build and construction, but accessibility is slightly different. Many motorcycle batteries are housed under the motorcycle seat or other body panels, so it can take some finesse to remove them.

Another thing that can weaken your battery connection is corrosion. Car batteries corrode as the sulfuric acid within the battery releases hydrogen gas. As the hydrogen gas interacts with air and other sources of moisture, it begins to build up on top of the battery and around the terminals.

To preserve your battery's electrical connection, an old remedy is using a mixture of 1.0 tablespoon of baking soda with 1.0 cup of water. This basic remedy will work quickly to neutralize the corroded acid. Tough corrosion may require using a wire brush to remove. After brushing, just spray it down with cool water and dry with a clean cloth. You can also apply a lubricant such as petroleum jelly to protect from future corrosion.

Car batteries are not one size fits all. When shopping for a car battery, make sure your replacement fits all the following criteria:

Group size is a number that should be listed on the battery itself. It refers to the dimensions of the battery and the size of the battery post it will fit. Below are common group sizes.

Group Size

Common Vehicle Fit

24/24F(top terminal)

Acura, Honda, Lexus, Nissan, Toyota

35(top terminal)

Mazda, Nissan, Subaru, Honda, Toyota

47/H5(top terminal)

Buick, Chevy, Volkswagen

48/H6 (top terminal)

Audi, BMW, Cadillac, GMC, Jeep, Mercedes-Benz, Volkswagen, Volvo

49/H8(top terminal)

Audi, BMW, Mercedes-Benz, Hyundai

51R (top terminal)

Honda, Nissan

65 (top terminal)

Large vehicles and SUVs

Whether you’re working with a new battery or an old one, disconnecting the negative cable first can help avoid electrical shortages.

Yes, it is OK to disconnect one terminal of a car battery as long as it is the negative battery terminal.

Disconnecting the battery will require items like pliers, a socket wrench, and maybe even an adjustable wrench or clamps depending on the terminal mount.

Corrosion hinders the amount of energy that can pass through battery terminals, leading to a drop in power.

You can charge a car battery using the following steps: prepare the battery, remove negative then positive cables, clean the battery terminals, connect the car battery charger, and test your car battery.

*Data accurate at time of publication.