How to jump start a car safely: step-by-step UK guide

Car Maintenance9/29/2026

How to Jump Start a Car Safely: Step-by-Step Guide | Rooster

To jump start a car, connect the jump leads in this order: red clamp to the positive (+) terminal of the flat battery, the other red clamp to the positive terminal of the good battery, black clamp to the negative (−) terminal of the good battery, and the final black clamp to bare, unpainted metal on the flat car, away from the battery. Start the working car, let it run for a few minutes, then start the flat car.

The order matters. Batteries can give off flammable gas, and connecting the last clamp away from the battery keeps any spark clear of it. Done wrongly, jump starting can also damage the batteries, the alternator and the leads.

This guide covers the equipment you need, the safety checks to do first, a step-by-step method, what to do afterwards, what to do if it does not work, and the special rules for hybrid and electric cars.

Last updated 29 September 2026. The method was checked against RAC and AA guidance (see the sources at the end). Always follow your car’s handbook if it differs.

Key takeaways

Read the handbook first. Some cars have specific jump-start points or rules.
Connection order: red on the flat battery’s positive, red on the good battery’s positive, black on the good battery’s negative, black on bare metal on the flat car. Remove the leads in the reverse order.
Never let the clamps touch each other, and never connect the last clamp to the flat battery’s negative terminal.
Do not use a hybrid or electric car as the donor unless the manufacturer specifically permits it.
Do not jump start a battery that is damaged, cracked or leaking.
If the car has not started after two or three attempts, stop and call for help.

What you need to jump start a car

Jump leads in good condition, with no frayed cable or damaged clamps. Heavier leads suit larger engines.
A second car with a healthy 12-volt battery, or a portable jump starter.
Your handbook, which shows where the battery or jump-start terminals are and any model-specific rules.
Gloves and eye protection, if you have them.
A torch if it is dark, and a hi-vis jacket if you are at the roadside.

Safety checks before you start

Read the handbook for both cars, as some models have special jump-start points or rules.
Look at both batteries and the jump leads. If either battery is cracked, leaking or frozen, or the leads are damaged, do not attempt a jump start.
Park the cars close enough for the leads to reach, but make sure they are not touching.
Switch off both engines, remove the keys, apply both handbrakes and put the cars in Park or neutral.
Turn off lights, the radio, air conditioning and other electrical items in both cars.
Remove rings, bracelets and watches, tie back loose clothing, and keep naked flames and cigarettes well away from the batteries.
Check that both batteries are 12-volt, which is standard for most cars.

The positive terminal is usually marked with a plus sign (+) and often has a red cover. The negative terminal is marked with a minus sign (−) and is usually black.

How to jump start a car, step by step

Prepare both cars. Follow the safety checks above, then open both bonnets. If the battery is in the boot or under a seat, check the handbook for the jump-start points.
Red clamp to the flat battery. Attach one red clamp to the positive (+) terminal of the flat battery.
Red clamp to the good battery. Attach the other red clamp to the positive (+) terminal of the good battery.
Black clamp to the good battery. Attach one black clamp to the negative (−) terminal of the good battery.
Last black clamp to bare metal. Attach the final black clamp to unpainted metal on the flat car, such as an engine bracket or bolt, away from the battery and from moving parts.
Check the connections. Make sure all four clamps are secure, the leads are clear of fans and belts, and the clamps are not touching each other.
Start the working car. Run its engine for a few minutes, typically two to five, so it can pass some charge to the flat battery.
Start the flat car. If it does not start straight away, wait a few minutes and try again. Do not crank for more than about ten seconds at a time.
Keep the engine running. Once the flat car is running, leave it running while you remove the leads.
Remove the leads in reverse order. Black clamp from the car that was flat, black clamp from the good car, red clamp from the good car, then the red clamp from the car that was flat. Never let the clamps touch each other while any are still connected.

Why not use the flat battery’s negative terminal? A charging or discharging battery can release hydrogen gas, which is flammable. Attaching the last clamp to bare metal away from the battery keeps any spark away from that gas.

What to do after a jump start

Keep the engine running and drive for a while, typically 20 to 30 minutes, so the alternator can recharge the battery. Short trips will not recharge it properly.
Avoid switching the engine off soon after the jump start, and avoid running heavy electrical loads such as heated seats and the rear screen until the battery has recovered.
Get the battery and charging system tested at a garage as soon as you can. A battery often lasts around three to five years, and a car that is jump started often has a battery that is ageing.
Check whether the clock, radio and other settings need resetting.

If the car will not start again the next day, the battery may be worn out, or the alternator may not be charging it. Our car battery guide explains how battery testing and replacement work, our guide to extending the life of your car’s battery has ways to avoid a repeat, and it is worth knowing what to do when the battery warning light comes on.

What if the car still will not start?

What you notice	Likely cause	What to do
Clicking, but the engine does not turn over	Poor connection, or a battery that is too flat	Check that all four clamps are firm and on clean metal, then let the working car run longer
Nothing at all, no lights	Bad connection or a battery beyond saving	Recheck the clamps and polarity; if still nothing, call for help
Starts, then dies soon after the leads come off	Failing alternator or a worn-out battery	Get the charging system tested
Starts, but is flat again the next day	Worn battery, or something draining it	Have the battery tested and ask about a parasitic drain
Engine turns over normally but will not fire	Not a battery problem: fuel or ignition	Stop trying and see why a car will not start

If the car has not started after two or three attempts, stop. Repeated attempts can overheat the starter and drain the donor car’s battery.

Jump starting a hybrid or electric car

Hybrid and electric cars have a 12-volt battery that runs the lights, computers and starting systems, alongside the high-voltage traction battery. You can usually jump start the 12-volt battery only, but you should always check the handbook first, because some models have specific jump-start terminals in the bonnet or fuse box.

Never connect anything to the high-voltage battery or its orange cables.
The RAC advises against using a hybrid or electric car as the donor vehicle unless the manufacturer specifically permits it, and the AA gives similar advice.
Use a conventional petrol or diesel car, or a portable jump starter, as the donor.
If you are not sure, call a breakdown service rather than risk damaging the car’s electronics.

Using a portable jump starter

A portable jump starter is a compact battery pack with its own leads. It lets you start a flat car without a second vehicle, which helps if you are alone or somewhere quiet. Follow the instructions supplied, because the steps can differ slightly from jump leads. In general:

Switch off the car, remove the key and turn off all electrical items, and make sure the pack is switched off.
Connect the red clamp to the positive (+) terminal of the flat battery.
Connect the black clamp to bare, unpainted metal on the car, away from the battery.
Switch the pack on, start the car, then switch the pack off and remove the clamps.
Keep the pack charged, because a flat jump starter is no use in an emergency.

Can you push start instead?

Only some manual cars can be push started, and it is not recommended for most modern cars. Automatics, hybrids and electric cars cannot be push started. Our guide on how to bump start a car explains the method and its limits, but jump leads or a breakdown service are usually the safer choice.

Common mistakes to avoid

Connecting the leads in the wrong order, or crossing positive and negative
Letting the clamps touch each other while they are connected to a battery
Attaching the last black clamp to the flat battery’s negative terminal
Using a hybrid or electric car as the donor when the manufacturer does not allow it
Trying to jump start a cracked, leaking or frozen battery
Ignoring the handbook, especially on newer cars with start-stop systems or batteries in the boot
Not finding out why the battery went flat in the first place

When to call a breakdown service

The battery looks damaged, or you can smell fuel or see smoke
You are in an unsafe spot, such as a live lane, a hard shoulder or a busy road
The car has not started after two or three attempts
You do not have leads, a donor car or a jump starter, or you are not confident doing it
The car is a hybrid or electric model and the handbook does not explain how to jump start it

A patrol can test the battery and alternator at the roadside and replace a worn battery. See why breakdown cover is a must-have for every driver, or find out more about Rooster Breakdown Assist.

How to avoid a flat battery

Have the battery tested before winter, especially if it is more than three years old
Take the car on a longer run, around 20 to 30 minutes, at least every week or two, rather than only short trips
Switch off lights and accessories before you leave the car
Keep the terminals clean and tight, and check for corrosion
If the car will be parked for weeks, consider a battery maintainer
Do not ignore slow starting, dim lights or a battery warning light

Frequently asked questions

Which jump lead goes on first?

Connect the red clamp to the positive (+) terminal of the flat battery first, then the other red clamp to the positive terminal of the good battery.

How long should you leave the cars connected?

Run the working car’s engine for a few minutes, typically two to five, before you try to start the flat one, and leave the leads connected while you do.

How long should you drive after a jump start?

Typically 20 to 30 minutes, ideally at a steady speed, so the alternator has time to recharge the battery. Short trips will not do the job.

Can jump starting damage a car?

Yes, if it is done incorrectly. The RAC warns that wrong connections can damage the battery, alternator and leads, so follow the correct order and the handbook.

Can you jump start a car in the rain?

Yes, with care. Keep the clamp connections as dry as you can, avoid standing in water, and check the handbook for any extra advice.

Can you jump start an automatic car?

Yes. Use exactly the same method with the car in Park, the handbrake on and the engine off. What you cannot do with an automatic is push start it.

How many times can you try to jump start a car?

Two or three attempts is a sensible limit. If the car has not started by then, the battery may be beyond saving or the problem may lie elsewhere, so call for help.

Why does my car keep going flat after a jump start?

The battery may be worn out, the alternator may not be charging it, or something may be draining it when the car is off. A garage can test the battery and charging system.

Sources and further reading

About this guide: Rooster is a UK car insurance provider. This guide is general information for UK drivers and is not a substitute for your car’s handbook or advice from a qualified mechanic or breakdown provider. If you are unsure at any point, call for help.

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