How to Jump Start a Car: Step by Step With Jump Leads or a Jump Pack

Published November 2026.

A flat battery is the most common reason a car won’t start, especially on the first cold mornings of winter. If you have jump leads and a second car, or a portable jump pack, you can usually be on your way in ten minutes. This guide shows how to jump start a car safely, the order to connect the leads, and what to do if it still won’t start.

Before you start: is it the battery?

Jump starting only helps if the battery is flat. Signs that it is:

• The engine turns over slowly, or you only hear a click when you turn the key or press start.
• The dashboard lights are dim or flicker, or don’t come on at all.
• The central locking or key fob didn’t work, and you had to use the key blade.
• The lights or something else were left on, or the car hasn’t been driven for a couple of weeks.

If the engine turns over at normal speed but won’t fire, the battery isn’t the problem, and a jump start won’t help. On a diesel, a glow plug light that stays on or flashes can point to a different fault.

What you need

• Jump leads (also called jump cables): a red lead and a black lead with a clamp at each end. Thicker leads carry more current and work better on bigger engines.
• A helper car with a working battery of the same voltage: almost every car is 12 volts.
• Or a jump pack (a jump starter or battery pack): a portable battery that does the job without a second car.
• Your car’s handbook. Many modern cars have dedicated jump points under the bonnet, sometimes away from the battery itself, and some makers have their own instructions.

How to jump start a car with jump leads

1. Park the helper car close, nose to nose or side by side, without the cars touching. Turn both engines off, take the keys out, and switch off lights, heater fans and anything else electrical.
2. Check the flat battery. Don’t jump start a battery that is cracked, leaking or swollen, or one that has frozen solid. Call for help instead.
3. Red to the flat battery’s positive (+) terminal.
4. Red to the working battery’s positive (+) terminal.
5. Black to the working battery’s negative (–) terminal.
6. Black to bare, unpainted metal on the flat car’s engine block or its marked earth point, away from the battery and from moving parts. Not to the flat battery’s negative terminal: a spark next to a battery can ignite the gas it gives off.
7. Start the helper car and let it run for three to five minutes, at a little above idle.
8. Start the flat car. If it doesn’t start, wait a few more minutes and try again. Don’t crank it for more than about ten seconds at a time.
9. Once it’s running, disconnect in reverse order: black from the earth point, black from the helper battery, red from the helper battery, red from your battery. Don’t let the clamps touch each other or the bodywork while any lead is still connected.

How to jump start a car with a jump pack

A jump pack (jump start battery pack) needs no second car, which makes it the easiest option on your own. Make sure it’s charged: many lose charge over a few months in the boot.

1. Turn everything off in your car.
2. Connect the pack’s red clamp to the positive (+) terminal or jump point.
3. Connect the black clamp to bare metal on the engine or the earth point (or the negative terminal, if the pack’s instructions say so).
4. Switch the pack on and start the car.
5. Switch the pack off, then remove black first and red second.

After the jump start

Keep the engine running and drive for at least 30 minutes, ideally on faster roads, so the alternator can put some charge back in. A short trip round the block often isn’t enough, and the car may not start next time.

If it goes flat again within a day or two, the battery may be worn out, or it isn’t being charged. Our car battery guide explains how to test it, how long batteries last and what a replacement costs. A battery warning light while driving usually means a charging fault: see our alternator replacement cost guide.

Common questions about jump starting

Can you jump start an automatic car?

Yes. You jump start an automatic in exactly the same way as a manual. What you can’t do is push or bump start an automatic, so jump leads, a jump pack or breakdown cover are your only options.

How to jump start a car without jump leads

Without leads, the options are a jump pack, a breakdown service, or, on a manual car only, a bump start: with the ignition on, second gear selected and the clutch down, the car is pushed to walking pace or more, and the clutch is released sharply. It’s harder than it sounds, needs a clear, safe space, and many makers advise against it on modern cars because of the risk to the catalytic converter. Never try it on an automatic.

Can you jump start an electric or hybrid car?

Electric and hybrid cars have a normal 12-volt battery that runs the electronics, and if it goes flat the car won’t switch on. Most can be jump started on that 12V battery or the jump points, following the handbook. Using an electric or hybrid car to jump start another car is a different matter: many makers say not to, so check first. Our hybrid guide explains how the different types work.

Does it matter which car has the bigger engine?

It helps if the helper car’s battery is at least as big as the flat one. A small petrol car can struggle to start a large diesel; leaving it connected longer before trying, or using a jump pack rated for diesels, usually solves it.

Frequently asked questions

Which jump lead goes on first?

The red lead, on the flat battery’s positive (+) terminal. Then red on the working battery’s positive, black on the working battery’s negative, and finally black on bare metal on the flat car’s engine.

How long should you leave jump leads on?

Run the helper car for three to five minutes before starting the flat car. Once it starts, disconnect the leads in reverse order straight away.

How long should I drive after a jump start?

At least 30 minutes, ideally at steady speed, to put charge back into the battery.

Can a jump start damage my car?

Done in the right order with the electrics switched off, the risk is very small. Connecting the leads the wrong way round can damage fuses and electronics, so check the + and – markings carefully.

Why won’t my car start even with jump leads?

The leads may not be making good contact, the helper car may need longer to charge the flat battery, or the battery may be beyond saving. If the engine turns over normally but won’t fire, the problem isn’t the battery.

Sources and related guides

• Car battery: how long it lasts, how to test it and replacement cost
• Dashboard warning lights: what every colour and symbol means
• Alternator replacement cost
• Mild hybrid vs full hybrid vs plug-in hybrid

Buying a used car this winter? Start with our free car check: MOT history, tax status and more, by registration.