How to Safely Jump Start a Car Battery

If your car will not start because of a flat battery, you can often get it going again using jump leads and a second vehicle with a fully charged battery. You will need a pair of quality jump leads and a donor car, and the whole process takes a few minutes once both vehicles are parked close together. If you are unsure at any point, it is safer to call a breakdown service or mobile mechanic.

• A second vehicle with a fully charged battery. Do not use a hybrid or electric vehicle as a donor unless the manufacturer specifically permits it.
• A pair of quality jump leads.
• A pair of rubber work gloves for safety.
• Both cars should have 12V systems and use the same type of system (most modern cars do).

1. Check both batteries and the jump leads for damage. Do not jump start if either battery is leaking, cracked, or badly corroded, or if there is visible damage to the surrounding area. Do not use damaged jump leads.
2. Remove any rings or metal jewellery you are wearing, and make sure nothing metal can touch the battery terminals. Never smoke or allow naked flames near either battery.
3. Switch off all electrical systems in the car with the flat battery, including lights, radio and sat-nav, and lower the driver's window if possible.
4. Park the donor vehicle as close to the casualty vehicle as possible without the vehicles touching, making sure the jump leads will comfortably reach from one battery to the other.
5. Switch off both engines, remove the ignition keys, and open both bonnets (or the boot if the battery is located there).
6. Attach one end of the red jump lead to the positive (+) terminal on the flat battery. The positive terminal usually has a red plastic cover with a plus (+) symbol.
7. Attach the other end of the red jump lead to the positive (+) terminal of the good battery on the donor vehicle.
8. Attach one end of the black jump lead to the negative (-) terminal of the good battery.
9. Attach the other end of the black jump lead to a good earth point on the casualty vehicle, such as a solid metal part of the engine, well away from the flat battery and fuel system.
10. Start the donor car and let it run for up to 5 minutes.
11. Try starting the car with the flat battery. Do not crank for more than about 5 seconds at a time, as this can overheat the starter. If it does not start, wait another couple of minutes and try again.
12. If it still does not start, there may be another fault, and you should call a breakdown service or mobile mechanic.
13. If the engine starts, leave it running for about five minutes.
14. Switch off the casualty vehicle and disconnect the leads in the correct order: remove the black lead from the earthed metal on the previously flat car, then the black lead from the negative (-) terminal on the donor car, then the red lead from the positive (+) terminal on the donor car, and finally the red lead from the positive (+) terminal on the previously flat car.
15. Keep the leads and clamps away from moving parts such as fans and belts as you remove them.

• Getting the connection order wrong can damage the car's electrics or cause sparks. If you are unsure, do not take risks.
• Do not remove the jump leads while the car engines are running, as this can cause serious damage to the cars' electronics.
• Stop using the jump leads if they get hot.
• Before you start, remove any dangling clothing such as a scarf or tie, as it could get caught in moving engine parts.
• Never let metal objects touch the car batteries, as this could cause a spark and possibly make the battery explode. This includes rings, necklaces, watch straps, hand tools, clips and stray wires.
• If your car will not start after a few attempts, there is probably a more serious problem requiring professional help.
• If you are not confident about jump starting, contact a professional mobile mechanic or breakdown service.

Can I use a hybrid or electric car as the donor vehicle? No, you should avoid using a hybrid or electric car as a donor vehicle unless the manufacturer specifically permits it, as this could cause damage.

What order do I connect the jump leads? Connect the red lead to the positive terminal of the flat battery, then the red lead to the positive terminal of the good battery, then the black lead to the negative terminal of the good battery, and finally the black lead to an earth point on the casualty vehicle.

How long should I leave the donor car running before trying to start the flat car? Start the donor car and let it run for up to 5 minutes before attempting to start the car with the flat battery.

How long should I crank the engine when trying to start it? Do not crank for more than about 5 seconds at a time, as this can overheat the starter. If it does not start, wait another couple of minutes and try again.

What should I do if the car still will not start after jump starting? If it still does not work, there may be another fault, and you should call a breakdown service or mobile mechanic.