Thursday, May 9, 2024

Which Battery Terminal To Disconnect When Working On Car

Don't Miss

Removing The Old Battery

Removing Car Battery Terminals

When removing the old battery, remember to first disconnect the cables from the negative terminal, which is usually black and has a minus sign then disconnect the cables from the positive terminal, which is usually red and has a plus sign. Take caution at all times to never touch a metal object to both terminals of the battery at once.

After disconnecting the terminals, unhatch the clamps securing the battery in place and slowly lift it out of the battery tray.

When Do You Need To Disconnect A Car Battery

Car batteries are one of the most crucial components of your vehicle, but you may need to disconnect them for a variety of reasons:

  • To perform maintenance on your vehicle: Some types of maintenance require you to disconnect the battery to prevent the risk of electrical issues or danger to yourself and your vehicle.
  • To replace or recharge the battery: Batteries need to be replaced from time to time , so disconnecting the battery would be mandatory for replacement. Additionally, if your battery is dead and cant be charged while seated in its holding tray, you would need to remove the battery and then charge it.

Switch Off The Ignition & Use Safety Equipment

Before you begin to disconnect the battery, ensure that the ignition is turned off and remove the key. Also leave the drivers door open, because it can happen that the car will lock while replacing the battery. If you have an automatic, check if the car is in Park position or it should be in the first gear in the case that the car has a manual transmission. Since the car battery holds an electric charge and is capable of releasing flammable gas as well, it is strongly recommended to put on some safety gloves and goggles.

Recommended Reading: Repairing Cigarette Burns In Car

It Prevents Corrosion On The Battery Terminals

One of the most important reasons to disconnect the negative battery terminal is to prevent corrosion on the battery terminals. Corrosion can cause a number of problems, including decreased battery life, decreased charging capacity, and even electrical shorts. All of these problems can be costly and inconvenient, so its important to take measures to prevent corrosion whenever possible.

All Memories Of Ecu Should Be Deleted:

12V Car Boat Van Battery Isolator Switch Brass Power Cut ...

When you want to reset the ECU of your car, the previous memories of the ECU should be forgotten or removed. So, when you disconnect the car battery, memories of the ECU start to disappear. It can take up to 5 to 15 minutes.

So, if you dont wait at least 15 minutes, some data might still be present on the ECU. The ECU will not be reset then. So, you have to reset it again.

Thats why if you want to reset the ECU effectively, you have to give it at least 15 minutes.

Don’t Miss: Clear Coat Coming Off Car

How To Hook Up Jumper Cables On Your Car

When your car won’t start, jumper cables can help your vehicle get up and running in just a few minutes. To hook up jumper cables, you typically need two cars. Pop both hoods, and then connect the red and black clamps to the battery in the car that won’t start. Then do the same to the other vehicle. Start the working car, and let it idle for a minute. Turn on the dead car, disconnect the cables from both vehicles, and you’re good to go!

Before you get started, however, you’ll need to know the right order to hook up the cables and what to do if you get it wrong. Find out how to hook up jumper cables and learn how to troubleshoot the process.

Do I Need To Disconnect Both Battery Terminals

You dont need to disconnect both of them, one will suffice. And whenever youre back, just connect it again. Chances are, your battery might still have some current left to start your vehicle and when your vehicle will run, itll recharge again.

Read Also: How To Wire A Car Radio To A House Outlet

Remove The Battery If Necessary

At this point, your battery should be entirely disconnected. However, you may need to remove the battery from the tray to perform maintenance or replace it with a new battery.

Your battery likely has a securing clamp over the top of the unit that holds it in place. The clamp will be secured with nuts of its own. Use a socket wrench to remove the nuts, then remove the securing clamp or lift it away from the battery.

You should be able to lift the battery out of the tray using your hands or with the handle attached to it . Most people who have never replaced a car battery are surprised to find out how much they weigh. Car batteries are pretty heavy, with most weighing anywhere between 30-50 pounds.

At this point in the process, the battery is disconnected from the engine and cannot power your vehicle. Youre free to perform maintenance or swap it out with a new battery, depending on your needs.

If you needed to remove your battery to perform a charge, you may now do so.

What Happens If You Only Disconnect The Positive Terminal First

How To Install A Car Battery Disconnect Switch

If you only disconnect the positive terminal, the battery will still discharge through the negative terminal. This will cause a voltage drop across the terminals and can reduce the life of your battery. It’s always best to disconnect both terminals to avoid any potential problems.

It’s always best to disconnect both terminals in order to avoid any potential problems. Disconnecting them in a different sequence won’t have an effect on your battery life however, it may cause an unnecessary voltage drop across the terminals which can lead to damaged equipment and reduced battery performance.

Don’t Miss: Florida Title Copy

Do I Need To Recharge My Car Battery

At the very least you should be recharging your battery every 6 months, even if you dont use your car every day. However, you can purchase a battery maintainer to plug in while you are not running your car, this will ensure the battery deteriorates at a healthy rate. Many people going overseas for a trip choose to enlist help from a friend to turn over the engine of their car and keep their battery healthy.

Clean The Battery Tray And Cable Connector

Once battery removal is complete, youll want to clean the battery tray and cable clamp or connector for future use. Do this irrespective of if youre 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.

Dont leave them hanging loose from your engine bay.

Whats next?

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

  • Secure the battery with the holding mechanism before reconnecting the terminals
  • Apply some anti-corrosion grease on each battery terminal and connector
  • When reconnecting the car battery, connect the positive terminal first, then negative

Note: Disconnecting and reconnecting a car battery isnt 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, lets go over some FAQs.

Also Check: Make Freshies

How Do You Position The Cars To Jump Your Battery

If your car’s battery is dead, you can jumpstart it with the help of a second vehicle. Pull the working vehicle up so the hoods of the two cars are just a few inches apart. Be sure to leave some space between them. The vehicles should be close enough so the jumper cables can reach between the two vehicles but not so close that the two cars touch.

For best results, the two car batteries should have a similar voltage. You can confirm that the numbers are the same or close by reading the specifications on the top of the batteries. If the working vehicle has a significantly higher voltage, jumping the battery could damage the other car. In that case, consider asking another driver to help instead.

Battery Terminals Should Be Cleaned

How to Disconnect a Car Battery â Mens Craze

Moisture can degrade some disconnected battery terminals over time. As a result, verify your automobile battery terminal once youve detached it. If you try to start the automobile after reconnecting the battery with a corroded terminal, the engine may not start due to low conductivity. As a result, before reconnecting the battery, make sure the airports are free of corrosion.

Also Check: Leasing Through Carvana

Can I Disconnect My Battery While The Car Is Running

This is a common backyard mechanic technique to test if your alternator is working properly. In theory, if your alternator is providing adequate power to the car while charging the battery, then once the car is started, disconnecting the battery should not cause the engine to stop running. If it does, then there is a possibility that the alternator is not producing enough electricity, or a connection to it is either not working or it is only working intermittently. HOWEVER, be aware that this test is not without risk to damaged car electronics.

If your alternator is malfunctioning by over-charging your battery, disconnecting it may allow the alternator to provide an even higher voltage to the car electronics, and potentially damage those sensitive components. Also, if the alternator is providing power intermittently, it may cause the computer lock up and produce other problems. Therefore, this test is safest if not performed at all. You are better to use a voltmeter, and measure the voltage at the battery when the car is off and when its running. In simple terms, if the voltage is higher when the car is running, then the alternator is providing at least some energy back to the battery, but that doesnt mean that its working optimally. Get it tested if you believe there is a problem.

Loosen The Nut On The Negative Terminal With A Wrench

Remove the plastic caps if your battery has them, then start looking for a wrench that fits the nuts and bolts for your battery terminals.

Unfortunately, no truly universal size applies to all terminal hardware, so its difficult to determine your wrench size without checking for yourself. Wed recommend bringing a wrench kit with multiple socket sizes for the task, so you have various options for finding the right one. You may need to try a few different socket wrench sizes before finding the perfect tool. Once you do so, place the wrench on the negative terminals nut and turn it counterclockwise to loosen.

Don’t Miss: Car Care One Stores

Uses For A Disconnect Switch

We mentioned it before, but the most significant factor when choosing a switch for yourself is what you are going to do with it.

Race Car Safety

Many sanctioned race bodies require a battery shutoff. Youll have to check with the rules for whatever event you are participating in. Be aware that sometimes safety tech wants the switch on the positive side.


The general idea behind using a battery disconnect for anti-theft is that a thief cant start the car and drive away if they have no power. The downside is that most disconnect switches are designed to be easy to get to, which means that the thief will be able to simply turn them back on.

If you are looking for anti-theft from a switch, get one that either has a hidden switch that activates a relay or that uses a key. That way, even if a thief can get your hood open, they cant simply hook the power back up.


You should generally disconnect your cars, boats, or lawnmowers battery before putting it into long-term storage. Most vehicles will have some parasitic loss. That loss comes from small devices or wiring issues that draw a tiny amount of energy from the battery. It may take those small leaks months to lower the voltage significantly, but they can kill a battery if left too long.

If you are storing something with a battery long-term, consider picking up a battery maintainer as well. We have an entire article about them over here.

Battery Isolation


Disconnecting A Negative Battery Terminal

How to disconnect a Car Battery Safely plus TOP TIP for keeping battery terminals corrosion free
  • Written by Piyush Jain on Nov 15, 2010To ensure our content is always up-to-date with current information, best practices, and professional advice, articles are routinely reviewed by industry experts with years of hands-on experience.Reviewed by

It is critical to disconnect a negative battery terminal before starting any work on your car – any car manual or auto mechanic will tell you that. The negative battery terminal is your ground, which keeps you from getting shocked when working on the engines, the electrical, and the fuel parts of your car. Disconnecting this terminal is a safety precaution that will help keep you from feeling the full power that surges through your car. Put mildly, its the number one safety precaution you can take before starting work on your vehicle.

To disconnect this terminal, follow the easy steps below.

Read Also: How To Reprogram Chamberlain Garage Door Opener

Disconnect The Battery Positive Cable

Once you have successfully disconnected the negative cable, the next is to disconnect the positive cable. Also, use the right wrench from your mechanic toolbox, turn the wrench counterclockwise to free the nuts. Avoid bridging the positive and negative terminal of the battery, as it could damage the battery or cause an explosion.

Ensure the positive terminal doesnt come into contact with the car chassis, the car electrical circuit could get disturbed because there could be some residual charges left in the system. It could also lead to electronic damage.

Step 4 Start Testing Again:

Once you know the current, its time to see if its safe to start charging again. If youre working on a car with a 12V system, youll want to measure the current again to make sure it hasnt changed. If it has, then you need to re-measure the current and make sure its safe to charge again.

The negative terminal of the battery is what keeps the positive side grounded. If the negative terminal were to become disconnected from the ground, the positive terminal would float in space and the engine would be unable to start.

This article will discuss why disconnecting the negative battery terminal is a good idea and how it can help with starting problems.

Read Also: Does Walmart Duplicate Car Keys

What Terminal Do You Disconnect When Working On A Car

Here is some information that can help you determine what type of connection needs to be disconnected and how it should be done, as well as why this procedure has been developed in the first place.

First, let’s look at why cars have two battery terminals. When a car is manufactured, the negative terminal of the battery is usually installed directly to the engine block or structure. This way, it can be grounded for safety purposes and because this method allows any potentially dangerous electrical currents to flow between these components very easily. The positive connection is made to the starter motor, and this is also why it’s usually recommended that you remove the battery cable from the starter before doing any work on the car battery.

The negative terminal should always be disconnected first since it’s connected to the ground. If you disconnect the positive connection first, there will still be a dangerous path for the current to flow, and it could easily cause an electrical shock.

If you’re not sure how to disconnect a car battery, it’s always best to take it to a mechanic or consult your owner’s manual. There are also many online tutorials that can show you how to do this safely. Remember, safety is always the number one priority when working on a car battery.

Which Battery Terminal To Disconnect First When Working On Car

Disconnect Battery Terminal with 5 Amp Fuse (BT5F)

Whilst there is no overt danger posed by mistakes when working with a car battery, its important to detach the negative terminal first. If you do this in the opposite order there are many problems that can arise from the extreme to the acute. When you disconnect a battery terminal, it is best to label the cable in some way to ensure you are always reconnecting the correct cable to the correct terminal on the battery.

Read Also: Florida Title Replacement

Disconnecting Needs To Be Completed:

If you disconnect the cars battery for a short time, disconnecting is not completed immediately. All the connections and current passing should be stopped when you disconnect the car battery to reset the ECU.

Especially when you want to disconnect the battery to reset the ECU, you need to wait for some time. Because current can be still present in the ECU. It can still have data and codes from the previous setting. Thats why you should wait at least 15 minutes after disconnecting the car battery.

When Should You Try To Start The Dead Vehicle

Image via Unsplash by jumpstarterexper.

After connecting all four ends of the jumper cables, turn on the working vehicle. Leave it in park and allow it to idle for at least a minute. Then attempt to start the other vehicle. If a dead battery was the issue, then the second vehicle should turn on right away.

You May Like: How Much Do Car Salesmen Make In Commission

How Does Disconnect The Negative Terminal Work

When connecting the negative terminal to the chassis, the negative terminal is usually secured by a nut and bolt. If this bolt is not tightened properly, it will allow the negative terminal to slide around on the chassis. This may cause the positive terminal to become disconnected from the ground.

If this happens, the engine will not be able to start because the positive terminal will float in space.

More articles

Popular Articles