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Jumper cables being connected to a car battery

How to Disconnect a Car Battery

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Handling Batteries Safely

Batteries create dangerous electrical currents. The fuel a battery uses is also sulfuric acid, which can burn you. Preparation and safety are paramount.

Disconnecting your car battery is essential before working on any electronics. However, you may need to remove it for other reasons, such as if it is not charging or the car will not start. Disconnecting a battery is a simple do-it-yourself task. However, there are steps you should take to ensure safety and that it is removed correctly.

Disconnecting the positive and negative cables

A typical car battery with positive and negative nodes

The positive and negative cables are cinched tightly to the battery terminals using connectors. First, you must determine which battery cable is positive and which is negative. There are two ways to figure this out. The negative cable is normally black, it should also have a negative or minus sign on both ends of the cable and a negative marking on the battery. The positive cable is usually red and may have a positive or plus sign on both ends of the cable and a positive marking on the battery.

One should never rely solely on the cable color to determine which cable is positive and which is negative. Always look for the positive and negative markings on the battery. Another way to determine the positive and negative terminals on the battery is by looking at the diameter of the battery posts. The positive battery post is always larger in diameter than the negative post. Always disconnect the negative cable first because it creates the electrical ground.

How the cable is secured to the battery posts will determine what tools are needed to remove it. Most terminal ends are secured with bolts. Using your wrenches, place on one each side and loosen the bolt. The bolt does not need to come all the way out. You may need to move the battery cable back and forth to loosen the clamp if it does not come off easily. Carefully place the negative battery cable away from the battery to avoid reactivating the electrical current. You can use a zip tie to hold the cable in place or place a cloth around it to prevent contact.

Remove the positive battery cable the same way and lay it aside.

Removing the brackets and screws

The battery fastens to a battery tray with brackets and screws. To remove the screws and brackets, use the socket wrench with an extended socket. Keep these screws and brackets to replace the battery.

Removing the battery

Car batteries can weigh up to 40 pounds. Hold the battery tight with both hands, lift it straight up and out of the battery tray. Carefully place it in a safe location. Batteries inevitably have acid on their exterior. Always wear gloves when removing a battery and do not let the battery come in contact with clothing or the vehicle exterior.

Cleaning the battery tray, cables, and terminals

Corrosion can prevent a car battery from working properly. Check the positive and negative battery terminals and the tray for corrosion.

A car battery with evidence of corrosion

Rather than replacing the corroded parts, try cleaning them first. Mix warm water and baking soda and spray it on any corroded parts. Use a wire brush to loosen the corrosion. Thick rust can be cleaned with a heavy duty anti-corrosion solution. Using a clean cloth, remove all cleaning agent. Make sure it is completely dry before replacing the battery. Always wear gloves and safety goggles when cleaning the battery cables and tray. If your battery terminals are badly corroded, the entire battery cable should be replaced. Use of emergency battery cable terminals is intended only for temporary use and not meant to be a permanent solution to a corroded cable end.

Locating the battery

Many car batteries are under the hood. Make sure your hood-stand is fastened securely to prevent it from coming down on your head. After the hood is properly secured, look to the front left or right to find the battery. If it is not visible, look for a battery cover near the engine. Carefully lift the battery cover if this is the case.

Some batteries may be located beneath hoses or other car parts. If it is not under the hood, then check the trunk. Look in the spare tire holder or above the rear wheel housing. In some vans, the battery is inside the cab, behind the dashboard or underneath the seat. The vehicle owner's manual will usually show the location of the battery.

Determining the battery type

There are three basic battery types which determine the position of the battery terminals. The three types of batteries are side post, top post, and batteries with both side and top posts. The kind of battery you have will determine what tools you need to remove it.

Gathering your tools

Before you begin to disconnect a car battery, you will need a few tools and essentials.

  • Crescent wrench and socket wrench
  • Automotive rags
  • Battery brush
  • Insulated gloves
  • Safety goggles
  • Anti-corrosion solution
  • Battery cleaner
  • Baking soda
  • Water

Installing a car battery

Again, safety is very important when working with a battery. Make sure the hood is secure before installing the battery. The battery is heavy, so make sure you lift it correctly.

Installing the car battery in its place

Pick the battery up and set it on the side of the car. Be sure to protect the fender with a fender cover or towel. Position the battery so that it is easy to connect the battery cables. Using the brackets and screws, secure the battery to the battery tray.

Always reconnect the positive battery cable first. Make sure the battery terminal is secure on the post before connecting the negative cable to prevent shorting any electronics then connect the negative cable. Again, make sure the terminal is tight on the post but be careful not to overtighten the terminals. If the cables are not tight, it can prevent the car from being able to start.

Staying Safe

Never work on your battery while the car is running and always disconnect the negative battery cable first and connect it last when replacing the battery. This is the first rule of safety when changing a battery.

When handling a battery always wear insulated gloves and safety goggles. The insulated gloves will protect your hands from accidental contact with battery acid and electric current. The goggles protect your eyes from battery acid if it splashes unexpectedly.

Remove any jewelry prior to touching the battery. The battery is designed to distribute voltage very quickly. Rings are especially dangerous if they encounter the voltage from a positive battery terminal. The amount of electric current a battery generates is enough to weld a ring to a positive terminal.

Storing and disposal

How you store your battery will determine the life of the battery. You must ensure the voltage stays at or above 12.4 volts. If you plan to reuse this battery, keep it in a cool, dry area and connect it to a battery maintainer. This device will make sure the battery stays charged. If a battery maintainer is not an option, you can leave it in the vehicle. Remove the cables and ensure they cannot come in contact with the battery or other parts of your vehicle. The vehicle can discharge the battery when it is not in use.

Keeping old batteries around is dangerous because they are filled with toxic acids. Most automotive stores offer a battery exchange program when you buy a new battery. Do not throw batteries in the trash. It is not only a hazard to the environment, it is illegal in some states. To find out where dispose of your old batteries, contact your local parts store or trash service.

Disconnecting your car battery is necessary for a number of reasons. Disconnecting it the right way is essential to prevent any harm to yourself or damage to your car’s electronic system. Always maintain safety and follow the proper procedures and you will be able to do this yourself. Ask an Expert if you still have questions about car batteries.

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