How to Jump-Start a Car Safely

When NOT to jump-start

Stop and call for help instead of jumping if you see any of these:

• A cracked, swollen, leaking or frozen battery
• Heavy corrosion, or a burning or rotten-egg smell
• Damaged, frayed or melted cables

A damaged battery can leak acid or, rarely, burst. It is not worth the risk — get it looked at.

Follow your vehicle’s own instructions

Many modern cars have a designated jump point under the hood rather than the battery itself, and the battery is sometimes in the trunk or under a seat. Your owner’s manual shows the correct points.

EVs and hybrids have a normal 12-volt battery for the electronics that can be jumped using the marked points — but never touch the high-voltage (usually orange) system, and follow the manual’s exact procedure. A hybrid should not be used to jump another car.

The safe order (12-volt petrol or diesel)

With both vehicles switched off and the keys out:

• Red clamp to the dead battery’s positive (+)
• Red clamp to the good battery’s positive (+)
• Black clamp to the good battery’s negative (−)
• Black clamp to a clean, unpainted metal point on the dead car (a bracket or bolt away from the battery) — not the dead battery’s negative

Start the good car, wait a minute, then start the dead one. Remove the clamps in the reverse order. Never let the two clamps touch each other.

After it starts

Keep it running or take a drive so the charging system can recover the battery. If it dies again soon after, the battery or charging system needs testing rather than another jump — see “Battery keeps dying”.

Safety

• Do not lean over the battery while connecting
• Do not create sparks near it (batteries can give off flammable gas)
• Do not let the clamps touch or short the terminals

General guidance, not a diagnosis — batteries, starting and charging systems have to be tested on the vehicle to be sure. Follow your owner’s manual, and never work around a damaged battery or a high-voltage (EV/hybrid) system.