How to Jump-Start a Car Safely, Step by Step
Short answer
Connect red to the flat battery's positive terminal, red to the donor's positive, black to the donor's negative, and the last black clamp to bare engine metal away from the flat battery. Start the donor car, then the flat one, and remove the leads in reverse order. A Tesla cannot be used as the donor car.
What is the correct order for the jump leads?
The order of the four clamps is the whole procedure, and the RAC and AAA describe it the same way. Both positive connections go on first, the donor negative next, and the final clamp goes on bare metal instead of the flat battery. Park the cars close without letting them touch, switch both off, and select Park or neutral with the handbrake on.
- Clamp one end of the red lead to the positive (+) terminal of the flat battery.
- Clamp the other end of the red lead to the positive (+) terminal of the donor battery.
- Clamp one end of the black lead to the negative (-) terminal of the donor battery.
- Clamp the last black clamp to bare, unpainted engine metal on the car with the flat battery, away from the battery itself.
- Start the donor car and let it run for a few minutes.
- Start the car with the flat battery.
- Remove the leads in reverse order: black from the engine metal, black from the donor, red from the donor, red from the car you revived.
Why does the last clamp go on engine metal?
The last connection is the one that can spark, so it is made away from the battery. A lead-acid battery can give off hydrogen, which is flammable, and a spark at the terminal is the risk the earth point avoids. Pick solid bare metal well clear of fuel lines, belts and the fan.
What should you check before connecting anything?
- Read the jump-starting page in the owner's manual. Cars with the battery in the boot or under a seat often have dedicated posts under the bonnet.
- Leave the battery alone if the case is cracked, leaking or swollen.
- Match the voltage. A 12 V car must not be jumped from a 24 V truck.
- Keep the free clamps from touching each other or the bodywork once the other end is connected.
- Switch off lights, air conditioning and audio in both cars.
What should you not do on modern cars, hybrids and EVs?
Modern cars carry control units that do not tolerate a reversed connection. Crossing the leads even briefly can blow fuses or damage electronics, so check each clamp against the + and - marks before the last one goes on. Many BMW, Audi, Volkswagen and Land Rover models have a sensor on the negative terminal. On those, use the earth point shown in the manual so the monitoring system registers the charge.
| Vehicle | Can it receive a jump? | Can it be the donor? |
|---|---|---|
| Petrol or diesel car | Yes, using the sequence above | Yes |
| Start-stop car with AGM or EFB | Yes; use the under-bonnet posts where fitted | Yes |
| Toyota Prius and similar hybrids | Yes, at the dedicated jump terminal in the fuse box | Check the owner's manual first |
| Tesla | Low-voltage battery supported from an external supply at the jump posts | No, according to Tesla's owner's manual |
| Other EVs | Varies by model; follow the manual | Varies by model; follow the manual |
A hybrid is boosted at the point the maker provides, not at the battery. Toyota states in its owner's manual that a flat 12 V battery stops the hybrid system from starting even with a full traction battery, and the Prius has a dedicated jump terminal in the fuse box for that reason. On any hybrid or EV, never touch the orange high-voltage cables.
A Tesla is the clear exception on the donor side. Tesla's owner's manual states that the car cannot be used to jump-start another vehicle. Its own low-voltage battery, lead-acid on older builds and lithium-ion on newer ones, is supported from an external supply at dedicated jump posts, and only to open the car and wake its systems.
What should you do after the engine starts?
A jump start gets the engine running; it does not refill the battery. AAA notes that even 30 to 60 minutes of running will usually not fully recover a battery after a complete drain, so a proper charge or a test should follow. If the engine stalls when the leads come off, Firestone Complete Auto Care points to the alternator, and the car should not be driven far.
Find out why the battery went flat. Lights left on overnight is a one-off. A battery that drains without a reason, or needs a second jump within days, is near the end, and workshop managers quoted in Gulf News say most last only a couple of years in the UAE. A load test settles it: 9.6 V or more for 15 seconds at half the CCA rating.