Quick answer
Connect red to the flat battery’s positive, red to the good battery’s positive, black to the good battery’s negative, and the last black clamp to bare metal on the flat car’s engine or body, away from the battery. Start the good car, wait a few minutes, then start the flat car. Remove the leads in the reverse order. Check your owner’s manual first: some cars have dedicated jump points, and some hybrids and EVs have specific rules.
Is this a DIY job?
- Difficulty: Easy
- Time: 10 to 20 minutes
- Tools: jumper leads (heavy duty) or a portable jump starter, safety glasses, gloves, owner’s manuals for both cars
- Skills: following a sequence carefully
Jump starting is a normal roadside job, but getting the order wrong can cause sparks, damage electronics or, rarely, make a battery explode. Take your time.
Step by step
- Check the manuals. Find the jump points for both cars. Some cars have remote jump terminals under the bonnet because the battery is in the boot or under a seat. Check whether either car is a hybrid or EV and what the manual allows.
- Check the batteries. Don’t jump start if either battery is cracked, leaking, swollen or badly corroded. Both systems must be the same voltage (almost all cars are 12V).
- Position the cars. Bring the good car close enough for the leads to reach, without the cars touching. Handbrakes on, automatics in Park, manuals in neutral. Both ignitions fully off, and switch off lights, radio and A/C.
- Protect yourself. Safety glasses and gloves on, rings and metal watch bands off. No smoking or flames. Keep leads away from fans and belts.
- Connect red to the flat battery’s positive (+).
- Connect the other red clamp to the good battery’s positive (+).
- Connect black to the good battery’s negative (−).
- Connect the last black clamp to bare metal on the flat car, such as an unpainted bolt or bracket on the engine, well away from the battery and moving parts. Don’t connect it to the flat battery’s negative post: the final connection can spark, and batteries can give off hydrogen gas.
- Start the good car and let it run for a few minutes.
- Start the flat car. Crank for no more than about 5 seconds at a time. If it doesn’t start, wait a couple of minutes before trying again. If it still won’t start after a few tries, the problem may not be the battery. (see Is it my starter motor or my battery?)
- Remove the leads in reverse order: black from the flat car’s earth point, black from the good battery, red from the good battery, red from the flat battery. Don’t let the clamps touch each other or any metal.
- Keep the jumped car running for a while, then have the battery charged properly and tested. Driving alone often won’t fully recharge a flat battery, and a battery that went flat for no clear reason may be failing or have a drain. (see Why does my car battery keep going flat?)
Using a portable jump starter
Follow the pack’s instructions. Most connect red to positive and black to an earth point or the negative post, with built-in reverse-polarity protection. Keep packs charged and stored out of direct sun, and avoid leaving lithium packs in a hot parked car. Don’t use a pack that is swollen, damaged or overheating.
Specs table
Connection order
| Step | Clamp | Connect to |
|---|---|---|
| 1 | Red | Flat battery positive (+) |
| 2 | Red | Good battery positive (+) |
| 3 | Black | Good battery negative (−) |
| 4 | Black | Bare metal earth point on the flat car, away from the battery |
Removal order: 4, 3, 2, 1 (the reverse).
What you’ll need
- jumper leads heavy duty or portable jump starter
- safety glasses
- smart battery charger (to recharge the battery properly afterwards)
When to call an auto electrician
- Either battery is damaged, leaking, swollen or smells of rotten eggs.
- The car won’t start even with a good jump.
- The car needs jump starting regularly.
- Warning lights stay on after the car starts.
- You’re not sure where to connect on a hybrid, EV or car with a battery in the boot. Never connect to or touch high-voltage parts or orange cables. Don’t use a hybrid or EV as the donor car unless its manual says that’s allowed.
- If you’re not confident, call your roadside assistance provider.
Need an auto electrician? Find local auto electricians and mobile services in your city.
Related questions
Q: Why not connect the last clamp to the flat battery’s negative post? A: The last connection often makes a small spark. Batteries can give off hydrogen gas, so the spark should happen away from the battery, on bare metal on the engine or body.
Q: How long should I leave the car running after a jump start? A: Long enough to be sure it keeps running, then have the battery charged with a proper charger and tested. A short drive won’t fully recharge a flat battery.
Q: Can I jump start a hybrid? A: Usually, yes, using the 12V jump points shown in the manual. The 12V battery powers up the system; you’re not jump starting the high-voltage battery. Follow the manual exactly.
Q: Can jump starting damage my car? A: Done correctly, it rarely does. Reverse polarity, clamps touching, or connecting with ignitions on can damage electronics. Some vehicle manuals give specific warnings, so check yours.
Sources
- RACV, “Car battery guide: how they work, when to replace them, and how to jump-start” – connection order; last clamp on unpainted metal on the flat car, not the flat battery’s negative; remove in reverse order. https://www.racv.com.au/royalauto/transport/cars/car-battery-guide-how-to-know-if-it-needs-replacing.html (checked October 2026)
- RAC (UK), “How to jump start a car in 10 steps” – crank limits, damaged battery warnings, hybrid donor caution. https://www.rac.co.uk/drive/advice/car-maintenance/how-to-jump-start-a-car/ (checked October 2026)
- ACCC Product Safety Australia, “Lithium-ion batteries guide” – store out of direct sunlight, not in hot places such as parked vehicles; don’t use swollen or damaged batteries. https://www.productsafety.gov.au/consumers/be-safe-around-the-home/safely-use-batteries-and-technology/lithium-ion-batteries-guide (checked October 2026)