How to jump-start a car
A flat battery can often be brought back to life with jump leads and a second car, or a portable booster pack. The order you connect the leads matters for safety.
- Time
- 20 to 30 minutes
- Difficulty
- Easy
- Steps
- 8
- Checked
What you’ll need
- Jump leads in good condition Search Amazon for jump leads car
- A second car with a healthy battery of the same voltage, or a jump starter booster pack Search Amazon for car jump starter pack
- Your car's handbook
- Gloves and eye protection (recommended)
As an Amazon Associate we earn from qualifying purchases. The Amazon links go to search results, so you can compare what’s available.
Safety first
- Never connect the black lead to the flat battery's negative terminal directly, or let red and black clamps touch. Both risk sparks and damage.
- Keep loose clothing, hair and hands away from the fan and belts once the engines are running.
- Don't smoke or use a naked flame near a car battery.
Step by step
-
Step 1: Check it's safe to jump-start
Read your handbook first. Some cars have specific jump-start points under the bonnet, and some say not to be jump-started at all. Don't jump-start if the battery is cracked, leaking or bulging. Don't use an electric or hybrid car to jump-start another car, as Which? warns this can damage its electrics and affect the warranty.
Next: step 2 -
Step 2: Position the cars
Park the working car close enough for the leads to reach, without the cars touching. Switch off both engines, put the handbrakes on, and turn off lights, radio and other electrics. Remove the keys from both ignitions.
Next: step 3 -
Step 3: Connect the red lead
Clip one end of the red lead to the positive (+) terminal of the working battery, then the other end to the positive (+) terminal of the flat battery.
Next: step 4 -
Step 4: Connect the black lead
Clip one end of the black lead to the negative (−) terminal of the working battery. Clip the other end to an earthing point on the car with the flat battery: bare, unpainted metal on the engine block or chassis, away from the battery. This avoids a spark near the battery, which can give off flammable gas.
Next: step 5 -
Step 5: Wait, then start the working car
Leave everything connected for 3 to 5 minutes, then start the working car and let it run for a couple of minutes.
Next: step 6 -
Step 6: Start the flat car
Try starting the car with the flat battery. If it doesn't start, wait a few more minutes and try again. Once it starts, let both cars idle for about 10 minutes with the leads still connected.
Next: step 7 -
Step 7: Disconnect in reverse order
Turn off both engines, then remove the leads in reverse: black from the earthing point, black from the working battery, red from the working battery, then red from the formerly flat battery. Don't let the clamps touch each other or any metal while connected.
Next: step 8 -
Step 8: Keep the battery charging
Restart your car and drive for at least 30 minutes so the alternator can recharge the battery. Avoid short trips straight away.
Tips
- A booster pack lets you jump-start without a second car. Check it's rated for your engine size and battery voltage, and keep it charged.
- If your battery goes flat more than once, get it tested. Many garages and tyre centres test batteries for free.
- Car batteries often fail in cold weather, so it's worth carrying jump leads in winter.
When to call a professional
Call your breakdown provider or a mobile mechanic if the car won't start after a couple of attempts, the battery is damaged, you're on a motorway hard shoulder, or you're not confident. A battery that keeps going flat may also point to a fault in the charging system.
Questions people ask
How long should I run my car after a jump-start?
Drive for at least half an hour, according to Which?, so the alternator can recharge the battery.
Can I jump-start a car in the rain?
Yes, as long as your leads are in good condition with no damaged insulation. Take extra care with connections.
Can an electric car be jump-started?
Many EVs have a 12V battery that can be jump-started like a normal car, but don't use an EV to jump-start another car. Check your handbook.
Sources
Checked 9 October 2026. We wrote this guide in our own words, using:
- Which?: how to jump-start your car safely (which.co.uk)
- Halfords: how to jump start a car (halfords.com)
Was this guide helpful?
Report a problem with this guide
Printed from howtoguides.uk/guides/how-to-jump-start-a-car/ · Checked 9 October 2026 · General information only. For gas, electrics, structural work, medical, legal or money decisions, use a qualified professional.