How to Disconnect Your Vehicle's Battery

Rich Ceppos
Photo credit: Getty Images

From Car and Driver

Your car won't start. You have a dead battery. We know, it's a pain! You'd like to pull it out and get it checked at an auto-parts store or maybe even replace it-and you want to do it yourself to save a few bucks.

If you haven't attempted to disconnect a battery before, we're here to help. It's simple and requires just a couple of tools. But you need to know how to do it properly to ensure your safety and make sure that nothing bad happens to your vehicle or its electrical system. Follow these steps and the operation will go smoothly and quickly.

Step 1: Locate the Battery

Most vehicles have them bolted in place under the hood. You'll have to get to it. If you've never raised your vehicle's hood before, check your owner's manual. It'll tell you how to do it and where the safety catch is under the front of the hood. Some vehicles have their batteries tucked away out of sight in the trunk. If you can't find your battery under the hood, it's almost for sure in the rear of the vehicle. Again, check your owner's manual to be sure.

Step 2: Locate the Positive and Negative Terminals

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This is one of the most important steps. The positive terminal is marked with a "+," and the negative is marked with a "-." Some batteries have plastic caps covering the terminals that will have to be removed for you to gain access to the battery cables-the wires connecting the battery to the rest of the vehicle-and the cable clamps that you will have to remove to disconnect the battery.

Step 3: Find the Right Wrenches

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You will need at most only a couple of wrenches to get the job done, depending on how much space there is to maneuver the wrench and whether the battery cable uses a single bolt on the clamp or one that also uses a nut on the other end. You'll have to borrow the wrenches from a friend or relative or buy a set. Most but not all battery-cable clamps have 10-millimeter bolts, so you'll likely need a 10-millimeter open-end wrench to disconnect the cables. A socket-wrench set that includes that same-size socket will be helpful as well. In some cases, you can get by with just an adjustable open-end wrench.

Step 4: Unbolt the Cables

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Here's where you need to be careful. Make sure the car's ignition is off. It's a good idea to wear eye protection when working around batteries. First, unbolt the negative battery cable and disconnect it by lifting it free. It might take some wiggling and twisting to pull it off. Be sure never to let the wrench touch both the negative and positive terminals at the same time. Even though the battery is technically dead, there might be enough residual electricity in it to short it out and create a spark, and you don't want any sparks around the battery or the engine compartment. There's also a remote possibility that shorting out the battery this way will damage your vehicle's electrical system or engine-control computer. After you've removed the negative cable, push it far out of the way. Now remove the positive cable.

Step 5: Remove the Battery Hold-Down Clamp

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Many batteries are secured by a clamp that locks the battery to the tray that it sits on. Before you can lift it out of the vehicle, you'll have to remove this clamp. This will likely require a socket wrench, possibly with an extension on it, as the bolts that hold the battery can be down low in the battery tray. Congrats, you've freed your battery!

If You're Storing Your Vehicle

A Final Note: If you're removing the battery cables to store your ride for an extended time, know that a fully charged battery will hold its charge for six months to a year if you disconnect the negative cable. If you're disconnecting the negative cable and leaving the battery in place, be sure to push the cable out of the way. If there's any chance that it might spring back into place and touch either battery terminal, use zip ties to hold it in place. Better still, buy yourself a battery-disconnect switch (it attaches to the negative terminal), which will serve the same purpose as removing the cables and will be there whenever you need it.

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