You might disconnect a car battery to replace it, to work on the electrical system, or to store the car. The process is simple, but order matters. This guide covers how to disconnect and remove the battery, then how to reconnect it. Your owner’s manual may include steps specific to your model.
Why the negative terminal comes off first
The car’s body is connected to the negative side of the battery. If a metal wrench touches the positive terminal and any metal part of the car while the negative is still connected, it can create a short and sparks. Removing the negative cable first breaks that circuit, so the risk drops when you work on the positive side.
What you need
- Wrench or socket, commonly 10 mm but sizes vary
- Safety glasses and gloves
- Zip tie, bungee cord or a clean rag to keep loose cables from touching the posts
Steps to disconnect the battery
- Park on level ground, turn the ignition fully off, remove the key and close the doors. Turn off lights and accessories.
- Open the hood and find the battery. Some vehicles have it in the trunk or under a seat or cover.
- Identify the terminals. Negative is marked with a minus sign and often has a black cable. Positive is marked with a plus sign and often has red.
- Loosen the nut on the negative clamp, lift the cable off and tuck it well away from the post. A rag or tie can hold it in place.
- Loosen and remove the positive cable the same way.
Steps to remove the battery
- Take off any cover, then undo the hold-down bracket or clamp.
- Lift the battery straight out while keeping it level. It is heavy, so bend your knees and consider a carrier strap.
- Check the tray and clamps for corrosion, and clean them if needed. Our step-by-step battery installation guide covers cleaning and fitting the new one.
- Do not toss the old battery. See how to dispose of and recycle an old car battery.
How to reconnect the battery
Reverse the order. Set the battery in the tray, secure the hold-down, connect the positive cable first and tighten it, then connect the negative and tighten it. Make sure both are snug and do not wiggle.
Common questions
Which terminal do you take off first? Negative.
Is it safe to disconnect the battery while the car is running? It is generally not recommended. On many modern cars it can cause electrical problems or damage electronics. Turn the engine off first.
How long do you need to disconnect it to reset the car? There is no single reliable figure, and it varies by vehicle. Check your manual or a dealer for your model, and note that disconnecting may not reset every system.
How long will a battery last disconnected? A disconnected battery slowly self-discharges, and the rate depends on its age, condition and temperature. For long storage, keep it in a cool, dry place and consider a maintainer made for car batteries.
Special cases
- Some cars lose radio presets, clock settings or learned idle settings when power is cut.
- Vehicles with start-stop systems, battery sensors or advanced electronics may need steps after reconnecting. Look in the manual.
- If you see swelling, cracks, leaks or a rotten-egg smell, stop and ask a professional.