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How to Disconnect a Car Battery

Power - by Joe Weber - updated on 8/24/2023

An employee disconnecting a car battery

Everyone who owns a car or truck will need to replace their battery at one point or another. While there are countless service centers and garages that will do this for you, it is always a good idea to learn how to do this yourself. Keep reading to learn the detailed steps of this process.

When Would I Need to Disconnect My Car Battery?

The obvious answer here is when you are replacing the battery. But there are a few more reasons why you would want to disconnect your car or truck battery.

To be safe, you should always disconnect the battery when you are working with anything electrical in the vehicle that could cause a spark or injury, like wiring, ignition work, airbags and the vehicle's computer. A sudden jolt of electricity to the airbag control could cause it to deploy and cause injuries, damaging the engine computer can end up costing thousands to replace. As a general rule, always disconnect the battery when working on electronics. Replacing light bulbs and things of that nature are safe to replace without disconnecting the battery.

How Do I Disconnect My Car Battery?

Before working with a car battery, remove all metal rings and jewelry to avoid creating a potentially dangerous situation if you accidentally make a connection between a hot (positive) and ground with your metal jewelry.

Prepare Your Workspace

  • Always wear safety glasses and gloves.
  • Gather all of the wrenches and other tools that will be required to remove the battery.
  • Have a car battery terminal protection kit ready to clean and protect the battery terminals and terminal connectors.

Disconnect the Battery

  1. Open and prop the hood of the car.
  2. Locate the battery and positive and negative battery terminals.
  3. Connect a memory saver to the OBD-II port in the car to preserve radio presets and other settings that may get erased after disconnecting the battery.

    This is not mandatory and if you don't have a memory saver, don't worry. You will just need to reset your radio presets and other settings after reconnecting the battery.

  4. Disconnect the negative cable from the battery first, then the positive terminal.
  5. Be sure to set the cables aside so they cannot come in contact with any metal or accidentally touch the terminals as you are removing the battery.
  6. Lift the battery out of the battery tray and place it in a safe place.
  7. Clean out any dirt and debris, like dirt and leaves, from the battery tray.
  8. Use a wire brush with the terminal cleaner spray to clean the battery terminals and connectors.
  9. Spray the terminal clamps and battery terminals with terminal protection spray to prevent any corrosion from building up.
  10. To reconnect the battery or install a new one, proceed to connect the battery terminals in the reverse order. Connect the positive (+) terminal first, then the negative.

For detailed steps on how to change a car battery please read our handy online guide "Simple Steps to Changing Your Car Battery".

Do I Need to Disconnect Both Battery Terminals When Charging?

With most modern chargers being automatic and microprocessor controlled it is not necessary to disconnect the battery in your car before charging it when using this type of charger. These chargers will automatically detect the battery's charge levels and adjust the amperage accordingly. Once the battery reaches the optimal charge, the charger will switch to a maintenance mode to keep the battery at a healthy level but it will not overcharge it.

If you are using an older charger or one that is not automatic it would be wise to disconnect the car battery completely from the vehicle prior to charging. Old chargers will not power off or switch to a maintenance mode when the battery is charged. It will continue to charge the battery as long as it is connected. It is very easy to overcharge a battery and reduce its lifespan. There are also some safety concerns with older chargers as they don't have reverse polarity protection. If you accidentally connect the clamps to the wrong terminal, bad things can happen, including damage to car electronics and even injury to yourself.

It is recommended that you have a good quality automatic charger in your arsenal to safely charge your car batteries.

Will the Car Battery Drain if the Negative Cable Is Disconnected?

Car batteries will self-discharge at a rate of 5-15% per month with at least the negative terminal disconnected. However, the alternative option of leaving the battery connected while it isn't being used will drain at close to 20% per week. That's a big difference and if you intend on not using the car for a longer period of time it is definitely worth disconnecting the negative battery terminal as the battery will discharge much more slowly.

Should a Car Battery Be Disconnected When Not in Use?

As you can see, storing your car batteries that aren't in use is best done disconnected from the car. When both terminals are connected, even though you are not using any of the electronics in the car, there is still a draw from the battery to power things like the clock, radio presets, etc. This draw will quickly leave you with a dead or dying battery that may need to be replaced if it sat long enough.

If you do intend to leave your car or truck sitting unused for long periods of time it is wise to add a battery maintainer to your list of tools.

What Is A Battery Maintainer?

A battery maintainer is essentially a small battery charger that sends small amounts of energy to the battery to keep it charged while it's being stored for a longer period. They help extend the life of the battery by preventing damage that can occur when leaving the battery sitting undercharged for a long period.

Using a maintainer while storing your batteries will ensure your battery is always charged at the optimum level.

Shop For New Car Batteries at Batteries Plus

If you are in need of a replacement car or truck battery look no further than Batteries Plus. Your local store offers free battery testing and installation (on most vehicles) if you need a new battery. Check out our large selection of car batteries today! Read more about our battery installation services in our blog articles titled "Does Batteries Plus Install Batteries?" and "Batteries Plus Offers Free Car Battery Installation".

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