Blog Car Care Advice How To Disconnect A Car Battery (Step-by-Step Guide)

How To Disconnect A Car Battery (Step-by-Step Guide)

June 7, 2021

Did you know that there’s a specific order that you need to follow when disconnecting your battery terminals?

In this article, we’ll show you how to disconnect a car battery safely, so that you don’t harm yourself or your car.

We’ll also go through some FAQs, including why you might need to disconnect the battery and an easy way to replace the car battery.

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Let’s dive right in.

How To Disconnect A Car Battery

Disconnecting your car battery is a fairly simple process. 

It involves these 5 steps:

However, before you get started, you’ll need some tools and safety measures in place:  

Tools Needed

Battery terminal bolts aren’t a standard size — they can be a single bolt, a clamp, or a bolt and nut pair. So it’s best to have a socket wrench kit or an adjustable wrench ready to cater to different sizes and forms. 

You may also want to have some anti-corrosion grease or rust spray on hand.

Safety Measures

Before beginning work on the car’s battery, here are some precautions to keep you and your vehicle safe:

Also, note that some electronics (like the clock, radio, or even the engine control module) may lose their settings without battery power. To prevent this, you may want to use a car memory saver to retain those settings. 

It’s also a good idea to check your car manual to see what electronics will be affected by the loss of battery power.

Once you’ve taken care of all of that, you can start disconnecting your battery by following these steps:

Step 1. Turn Off Ignition And Locate The Battery

Turn off the car’s ignition switch and remove the key. 

You’ll then need to locate your car battery. 

Most of the time, it’ll be in the engine bay. 

However, some batteries are located in the trunk or under a rear seat — making them a little harder to access. Refer to the car manual if you can’t find it.

Once you’ve located the battery, check it for corrosion, damage or leakage. 

If a car battery terminal is heavily corroded, disconnecting the cable clamp or connector from the battery post may be more challenging. Don’t try to force the connector off, as you could break the battery post. 

In this case, you’ll need to loosen some of the corrosion first. A solution of water and baking soda, and the aid of a wire brush, can help to clear corrosion. 

If you want a detailed walkthrough on how to remove corrosion, check out our battery corrosion guide.

If the car battery is damaged, bloated, or leaking, don’t work on it. 

Call a mechanic to deal with it instead, as you’ll likely have to replace it. 

Step 2. Disconnect The Negative Terminal First

Some battery terminals are covered with plastic caps that you’ll have to remove. 

The negative battery terminal is usually marked with a minus (-) symbol and has a black cap. The positive terminal typically has a plus (+) symbol and a red cap. 

When disconnecting a car battery, always remove the negative connector (negative clamp) from the negative terminal first. This is to avoid electric shocks or sparks. 

How do you disconnect it?

Gauge the size of the socket wrench you’ll need (it’s usually around 10mm), fit it over the connector bolt, and turn left (counterclockwise) to loosen. 

Important: Don’t ever let your wrench touch both terminals simultaneously, as you’ll create an electrical path.

Once the negative connector and negative battery cable have been released, remove them and keep them aside, away from the battery and positive terminal.

Step 3. Disconnect The Positive Terminal Second

After the negative terminal has been disconnected, do the same thing for the positive terminal. 

Loosen the positive connector and positive cable with the socket wrench, then keep them away from the battery and negative cable. 

Don’t let the positive connector touch any metal part of your car, as it can carry a residual current that may damage or disrupt vehicle circuitry. 

Step 4. Detach Holding Mechanism And Remove Battery

Most batteries are secured to the battery tray with some type of holding mechanism. This is usually a bracket or strap. 

Find the holding bolts and loosen them so you can detach the holding mechanism. Some bolts are close to the base of the tray, and you may need to reach further down with the socket wrench.

Batteries can be surprisingly heavy, often weighing between 40-60 lbs. 

Keep this in mind when you lift the battery off the battery tray.

If you’re removing a flooded lead-acid battery, make sure to lift it straight up to avoid sloshing the battery acid inside. 

Then, place the old battery on a level surface.

Step 5. Clean The Battery Tray And Cable Connector 

Once battery removal is complete, you’ll want to clean the battery tray and cable clamp or connector for future use. Do this irrespective of if you’re installing a new car battery or just taking the car battery out for a recharge. 

Clean the battery tray and connectors of any dirt and corrosion, then spray it with an anti-corrosion compound. 

Always make sure each battery cable is secured out of the way. 

Don’t leave them hanging loose from your engine bay.

What’s next?

If you plan to install a new battery or put back the current one, reverse the entire process: 

Note: Disconnecting and reconnecting a car battery isn’t difficult and is something you can do yourself with a little bit of care and attention. However, whenever in doubt, always get a professional to handle the task.

Now that you know how to disconnect and remove your car battery, let’s go over some FAQs.

5 Car Battery FAQs

Here are some answers to common car battery questions:

1. Why Would I Need To Disconnect The Car Battery?

There are many reasons for disconnecting the car battery from the engine bay. 

Here are some of the usual ones: 

A. Replacing A Faulty Battery

Putting in a new battery is one of the most common reasons for disconnecting the battery. 

Make sure the old battery is disposed of properly.

B. Recharging A Flat Battery 

You may want to use a battery charger to recharge a flat car battery. 

Sometimes you don’t have to remove the battery from the engine bay, but only disconnect the cables and hook the battery to the charger. 

If you’re uncertain about using a battery charger, get a mechanic to handle the task for you. You’ll also have the benefit of asking them to test it for you to find out why there’s a battery drain in the first place.

C. Cleaning Battery Corrosion

Corroded battery terminals should be cleaned, as corrosion affects battery performance and can shorten its life. 

It’s often a good idea to take out the battery from the engine compartment when cleaning to prevent corrosive elements and cleaning agents from falling on engine parts.

D. Performing Car Maintenance 

Some engine maintenance may require the battery to be disconnected or taken out of the way to access engine parts.

E. Storing A Car For An Extended Period

If you plan on storing a vehicle for an extended period, it’s advisable to disconnect at least the negative terminal from your car battery. This prevents unnecessary battery drain, as a fully charged battery can hold its charge for 6-12 months if you do this. 

Alternatively, you can use a battery disconnect switch (also known as a kill switch) which attaches to the negative terminal to cut the electrical connection. The battery disconnect switch makes an excellent anti-theft device for other times too. 

And finally, if you plan to leave your battery unused for a long time, you may want to attach it to a battery tender to help maintain its charge. This ensures that it can be up and running when you need it again.

2. What’s A Lead Acid Battery?

The lead acid battery is the most common car battery type. It can be in a wet cell (flooded) or a dry cell (gel or AGM) format. The battery generally consists of lead plates and battery acid (a mixture of water and sulfuric acid).

However, lead acid batteries aren’t the only type of battery out there.

Check out the different car battery types available.

3. What Does The Car Battery Do?

The main battery function in the car is to provide a spark to the starter to crank the engine. 

The car battery also provides power for every electrical component in your car — from the headlights to the onboard computer. 

When your car is running, the alternator recharges the battery. 

But when the engine is off, your battery is running on its own stored charge. This is why it’s essential to avoid unnecessary drain from any electrical system (like the headlights) when you’re not running the car. 

4. Can I Recharge A Dead Battery?

A successful recharge of a dead battery depends on how depleted the battery is. 

This is a good time to have a voltmeter or multimeter handy, so you can measure your battery voltage and have an idea of its state of charge. 

If the battery voltage is 12-12.4V, it still has about 25-75% of its charge, but not enough to start the car. 

In this case, you can pull out the jumper cable, jump start the car and take it for a drive to let the alternator recharge the battery. Minimize the use of any electronics and keep the car above idle as much as possible. Aim for about 30 minutes of driving. 

If the battery voltage is under 12V, the battery is fully discharged. You can still jump-start the car but charging with the alternator is not advisable when the car battery is this depleted. 

It’s a better option to use a dedicated charger to recharge a depleted car battery. Just be aware that a very old battery could be unrecoverable. 

5. What’s An Easy Way To Replace The Car Battery?

If your car battery fails, the battery warning light or check engine light will probably illuminate the dashboard. 

But there’s no need to panic. 

RepairSmith can help you sort out your battery issues and fit in a new battery if required.

What’s RepairSmith?

RepairSmith is a convenient mobile vehicle maintenance and repair solution. Here are some excellent reasons to keep them in mind:

Car battery replacement and fixes can be made right in your driveway

Battery replacement cost will vary based on car make and model, and location. For an accurate estimate of the cost, fill this online form.

Final Thoughts

Disconnecting a car battery isn’t hard to do. The most important thing to remember is that the negative terminal comes off first

And when you’re reconnecting the battery, just reverse the sequence. 
However, if you have other battery issues and want to be extra safe, just contact RepairSmith and let their ASE-certified technicians do the job, right in your driveway!