Whether you’re replacing an old battery or helping a friend jump-start their car, knowing how to safely connect, disconnect, and jumpstart a car battery can help you avoid injury, prevent damage, and get back on the road quickly. Stay safe and protect your car’s electronics with this simple step-by-step guide.
Quick Navigation
- What to Know Before You Begin
- How to Disconnect a Car Battery
- How to Connect a Car Battery
- How to Jump Start a Dead Battery
- When to Call the Pros
What to Know Before You Begin
These steps are intended to be a general set of guidelines when performing the tasks listed below. Always consult your vehicle's owner’s manual prior to attempting any of these services.
Some vehicles may require advanced tools to register the new battery, save the vehicle’s memory, or disable the high-voltage system. Some vehicles may need a code entered to resume radio functionality after battery replacement. Other vehicle types may have multiple batteries. If you're unsure, play it safe—book a service with your local Firestone Complete Auto Care.
How to Correctly Disconnect a Car Battery
1. Turn off Engine
Turn off the engine and all accessories. Never disconnect the battery while the engine is on. Doing so could lead to car damage and bodily injury.
2. Gather Your Tools
You may need the following items before disconnecting your car battery:
- Gloves
- Safety Goggles
- Socket Wrench or Wrench Kit
3. Locate the Battery
Most batteries are under the hood, but if you have difficulty locating yours, check your trunk or owner's manual.
4. Locate the Terminals
Now that you've found the battery, it's time to pinpoint the car battery terminals.
- Negative terminal: “–” sign or black cap
- Positive terminal: “+” sign or red cap
5. Disconnect Battery Cables (Negative First!)
The positive and negative battery cable ends each have a nut or bolt connecting them to their respective battery post. However, DO NOT disconnect the positive terminal before the negative one. Doing so can cause an electrical short.
Here's what you need to do:
- Using your socket wrench, loosen the nut on the negative battery terminal and remove it from the battery post.
- Set aside the cable — far away from the battery terminals.
- Repeat the above steps for the positive battery cable.
Safety Disclaimer: Ensure that your wrench doesn’t touch both terminals simultaneously. Doing so can cause electricity to pass through your wrench.
6. Loosen and Remove the Battery Hold-Down
You’ll likely find a strap or bolt-down wedge holding your battery in place. With your wrench, loosen the nut(s) and remove the battery hold-down.
7. Remove the Car Battery
Lift the battery out carefully. They’re heavy (up to 40 lbs!), so ensure your legs are prepared for the lift. Ensure the battery remains level when removing it from your vehicle to help prevent battery acid from sloshing around. Then, set the battery down on a flat, dry surface.
Note: Batteries may have small amounts of acid on them that could corrode anything they touch, including your clothing. So, be sure to sit the battery down on a non-conductive surface.
How to Connect a Car Battery Correctly
Your negative and positive cables are a good distance from the battery terminal. Your battery is lying on a flat surface. And most importantly, you’re safe because you were careful when removing your car’s battery.
If you can check all those boxes, then you’re ready to learn how to safely connect a car battery!
1. Clean Cable Contacts and Battery Terminals
Your replacement battery (or existing one if it’s still good) should not be installed until the cable contacts and terminals are corrosion- and debris-free. Clean the posts and cable ends using a mixture of baking soda and water with a wire brush or battery cleaner.
2. Place the Battery in Its Compartment
Now for the fun part: learning how to connect a car battery properly. Lift your new battery (remember to keep it level) and set it in the battery tray or compartment.
3. Secure the Battery
Reattach the hold-down hardware to keep it snug.
4: Reconnect the cables — positive first.
Attach and tighten the positive cable first, followed by the negative one.
How to Connect Jumper Cables to a Car Battery
You never know when you may need a jump-start or when someone needs you to power back up their car. Neither scenario tends to happen at a convenient time. But at least if you know how to connect jumper cables, the process can be over sooner rather than later:
- Attach the positive clamp (red or yellow) to the dead battery’s positive terminal. Ensure that the other nearby negative clamp (black) doesn’t touch the positive clamp nor any other part of the car or engine.
- Attach the clamp at the opposite end of the positive cable to the good battery’s positive terminal.
- Attach the negative clamp (black) to the good battery’s negative terminal.
- Attach the clamp at the opposite end of the negative cable to an unpainted metal surface such as a bolt, bracket, or engine mount—away from the battery of the discharged vehicle.
Time to Jump-Start
Once your cables are properly in place (and not hanging over any belts or pulleys that will rotate when the engine starts), it’s time to jump-start the car. Follow these steps:
- Start the good battery car’s engine so it can give the dead battery some juice.
- Wait about 5 minutes before starting the bad-battery car’s engine.
- Allow the bad-battery car’s engine to stay on for 20 to 30 seconds to confirm it won’t stall.
- Disconnect the cables in the reverse order you connected them. (Note: As you disconnect the clamps, don’t let the negative clamps touch the positive clamps or any other part of the car or engine until all 4 clamps are removed.)
When to Call the Pros
Replacing a battery can be straightforward, but it’s not always simple. Some modern vehicles require battery registration or memory-saving devices to avoid system resets. And no one wants to deal with fried fuses or lost radio functions.
If you'd rather not take the chance, let Firestone Complete Auto Care handle it. Our pros can test your current battery, help you choose the right replacement, install it safely, and properly dispose of your old battery. See if services are available in your area, and schedule your appointment today!
