Which cable do you connect first on a battery?

Connect the red (positive) cable first, then the black (negative). When disconnecting, remove the black (negative) first, then the red (positive). This sequence reduces the risk of sparks and short circuits, and it’s the standard practice for car batteries and most 12V automotive systems.

Why the order matters

Car batteries can release hydrogen gas, and a spark near the battery can ignite it. Connecting the positive (red) first keeps the circuit open until you attach the negative, minimizing the chance that a tool or clamp accidentally bridges the positive terminal to grounded metal. When removing cables, taking off the negative (black) first breaks the circuit and makes accidental shorting far less likely.

Step-by-step: jump-starting a vehicle safely

The following steps outline the safest standard method to jump-start a conventional 12V vehicle using booster cables. Always consult both vehicles’ owner’s manuals for model-specific procedures and designated jump points.

1. Park the vehicles close but not touching. Turn off engines, lights, and accessories. Engage parking brakes and open hoods. Wear eye protection.
2. Identify battery/jump posts: positive (+) often has a red cover; negative (−) is usually bare or marked black. Many modern cars provide remote “+” and “−” posts under the hood—use those if provided.
3. Connect red clamp to the dead vehicle’s positive (+) terminal or positive jump post.
4. Connect the other red clamp to the donor vehicle’s positive (+) terminal or jump post.
5. Connect black clamp to the donor vehicle’s negative (−) terminal or negative jump post.
6. Connect the remaining black clamp to an unpainted, solid metal ground on the disabled vehicle (such as an engine lifting point or designated ground stud)—not to the dead battery’s negative terminal. This reduces spark risk at the battery.
7. Start the donor vehicle and let it run for 2–5 minutes to stabilize voltage.
8. Attempt to start the disabled vehicle. If it doesn’t start, wait another couple of minutes and try again. Avoid cranking for more than 10 seconds at a time; let the starter cool between attempts.
9. After the disabled vehicle starts, leave both engines running for a minute.
10. Disconnect cables in reverse order: remove the black clamp from the grounded metal on the previously dead vehicle.
11. Remove the black clamp from the donor vehicle’s negative (−) terminal.
12. Remove the red clamp from the donor vehicle’s positive (+) terminal.
13. Remove the red clamp from the previously dead vehicle’s positive (+) terminal.

Once disconnected, keep the revived engine running for at least 15–30 minutes or drive the vehicle to recharge the battery. If problems persist, test the battery and charging system.

Disconnecting and reconnecting a single battery

If you’re removing or installing a 12V car battery (not jump-starting), follow these basic sequences to prevent accidental short circuits and protect electronics.

1. Turn off ignition and all accessories; remove the key. If using a memory saver, connect it per instructions before disconnecting the battery.
2. Loosen and remove the negative (black, −) cable first; secure it away from the battery.
3. Loosen and remove the positive (red, +) cable second.
4. Remove any hold-downs and lift out the battery safely.

With the negative cable removed first, you minimize the risk that a tool touching the positive terminal and bodywork creates a dangerous short.

When installing or reconnecting, reverse the order for safety and correct system initialization.

1. Place and secure the battery. Confirm polarity alignment (+ to +, − to −).
2. Attach and tighten the positive (red, +) cable first.
3. Attach and tighten the negative (black, −) cable second.
4. Start the vehicle and check for warning lights. On some cars, you may need to initialize windows, sunroof, or steering angle sensors.

If your vehicle has a battery management system, follow the manufacturer’s procedure; some vehicles require “battery registration” with a scan tool after replacement to ensure proper charging.

Common mistakes to avoid

These frequent errors can cause damage or injury. Keeping them in mind will help ensure a safe connection every time.

• Reversing polarity (clamping red to − or black to +). This can instantly damage electronics.
• Making the final connection on the dead battery’s negative post, which increases the chance of sparks near battery gases.
• Letting clamps touch each other or metal bodywork while connected to a live battery.
• Skipping eye protection or working near open flames/smoking around batteries.
• Ignoring manufacturer-designated jump points or intelligent battery sensors; many modern cars require using a specific ground stud instead of the negative terminal.
• Cranking the starter repeatedly without allowing cool-down, risking starter or cable damage.

A few extra seconds spent checking polarity, clamp placement, and manufacturer guidance can prevent costly mistakes.

Special cases and modern vehicles

Some vehicles have additional requirements. Review your owner’s manual before connecting or jump-starting.

• Hybrids and EVs: Do not jump or connect to the high-voltage battery. Use only the designated 12V jump posts and follow the manual.
• Start-stop systems (AGM/EFB batteries): Use the correct battery type and consider battery registration after replacement to avoid charging or idle-stop faults.
• Intelligent Battery Sensor (IBS): Common on the negative terminal; use the vehicle’s specified ground/jump post so the sensor measures current correctly.
• 48V mild hybrids: Never connect jump leads to 48V components. Use the 12V system jump points only.
• Accessories and memory: If preserving radio codes or settings matters, use an approved memory saver; follow safety guidance to avoid shorts.

Adhering to these model-specific rules helps protect sensitive electronics and ensures the vehicle charges correctly.

Quick reference

Use this at-a-glance guide to remember the correct order for cables.

• Connecting: red (positive) first, black (negative) second.
• Disconnecting: black (negative) first, red (positive) second.

Keep this sequence in mind for both jump-starting and routine battery service unless your vehicle’s manual specifies a different procedure.

Summary

Connect red first, then black; disconnect black first, then red. This established sequence minimizes spark and short-circuit risks, protects electronics, and aligns with modern vehicle safety practices. Always follow your owner’s manual, use designated jump points, and avoid making the final connection on the dead battery’s negative terminal.