Written by the Silicon Oasis Car Battery team ·
Key points
- Read your owner's handbook first. Many cars have dedicated jump-start points and specific instructions.
- Never jump start a battery that is swollen, cracked, leaking or smells of rotten eggs.
- The last connection goes to bare metal on the engine or body, away from the battery, not to the flat battery's negative terminal.
- Afterwards, drive for 30 to 45 minutes and have the battery tested.
Before you start
- Check the battery. If the case is bulging, cracked or wet, or you smell rotten eggs, do not go further.
- Check the handbook of both cars. Some manufacturers forbid using the car as a donor, and many hybrids and electric cars must not be used to jump start another vehicle.
- Switch off both ignitions, lights and accessories. Put both cars in park or neutral with the handbrake on.
- Keep metal jewellery, loose clothing and the lead clamps clear of each other and of moving parts.
- Make sure the two cars are not touching.
Batteries give off hydrogen, which is flammable, and contain sulphuric acid. No smoking or flames near the battery, and protect your eyes. This guide is general information. Your car's handbook takes priority, and if anything is unclear, call a professional.
Jump starting with jump leads and another car
- Connect one red clamp to the positive (+) terminal of the flat battery, or to the car's positive jump-start point.
- Connect the other red clamp to the positive (+) terminal of the donor battery.
- Connect one black clamp to the negative (−) terminal of the donor battery.
- Connect the last black clamp to an unpainted metal part of the engine or body of the car with the flat battery, or to its marked earth point, well away from the battery.
- Start the donor car and let it run for a few minutes.
- Start the car with the flat battery. If it does not start within a few seconds, wait a minute before trying again.
- Once it is running, remove the leads in exactly the reverse order: black from the earth point, black from the donor, red from the donor, red from the car that was flat.
Jump starting with a booster pack
- Make sure the pack is charged and switched off.
- Connect the red clamp to the positive (+) terminal or jump-start point.
- Connect the black clamp to the earth point the pack's instructions specify.
- Switch the pack on and start the car.
- Switch the pack off and remove the black clamp, then the red.
A good booster pack has reverse-polarity and surge protection, which removes the two most common causes of damage. It also needs no second car, which matters in a tight basement bay.
When not to attempt a jump start
- The battery is damaged, leaking or smells of sulphur.
- You cannot find the battery or the jump-start points. On many cars the battery is in the boot or under a seat.
- The car is a hybrid or electric car and you are not certain of the 12V procedure. Never touch orange high-voltage cables.
- The car has already been jump started more than once recently. The battery or charging system needs testing, not another boost.
- You are at the roadside without a safe place to stand.
After the engine starts
Drive for 30 to 45 minutes without stopping, roughly 15 to 20 km. A two-minute trip does not replace the charge. Then have the battery and alternator tested: a battery that went flat for no obvious reason will usually do it again.