How to Jump Start a Car: The Complete UK Guide

Summary

• Red to dead, red to good, black to good, black to metal: This is the safe order for connecting jump leads.
• Keep engines running: Let the donor car run for a few minutes before trying to start the dead car.
• Drive for 30+ minutes: After jump starting, drive to recharge the battery. Check out our car battery guide for more tips.

It's Monday morning. You're already running late. You turn the key and... click, click, click. Nothing. Your heart sinks.

A flat battery is one of the most common car problems in the UK. The good news? It's also one of the easiest to fix. With a set of jump leads and a helping hand, you can be back on the road in about ten minutes.

Let's walk through exactly how to jump start a car safely. No confusing jargon. Just clear steps you can follow.

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What You'll Need to Jump Start a Car

Before you start, make sure you have:

• Jump leads: A pair of heavy-duty cables with crocodile clips. Red is positive. Black is negative.
• A donor car: Another vehicle with a working battery. The battery should be the same voltage (almost all cars use 12V).
• A safe location: Park both cars close together but not touching. Make sure you're away from traffic.

Don't have jump leads? A portable jump starter pack is a handy alternative. They're small, rechargeable, and let you jump start without another car. Keep one in your boot for emergencies.

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Safety First: Before You Touch Anything

Batteries contain acid and produce explosive gases. This isn't to scare you. It's to make you take simple safety steps seriously.

Before You Start

• Remove metal jewellery like rings and watches. They can cause sparks.
• Don't smoke near the batteries. Ever.
• Check both batteries for damage. Look for cracks, leaks, or corrosion. If you see damage, don't attempt a jump start.
• Turn off both engines and remove the keys.
• Turn off all electrical items in both cars. This includes lights, radio, and heating.

A Word on Modern Cars

Some newer cars have batteries in unusual places, like the boot or under the rear seat. However, they'll usually have jump start terminals under the bonnet. Check your owner's manual if you're unsure.

Some manufacturers also warn against jump starting their vehicles. This is rare, but it's worth checking your handbook. If in doubt, call your breakdown service instead.

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How to Jump Start a Car: Step-by-Step

Right. Let's get your car started. Follow these steps in order.

Step 1: Position the Cars

Park the donor car close to your dead car. The batteries need to be near enough for the jump leads to reach. The cars should not touch each other.

Apply the handbrake on both vehicles. Put both cars in neutral (or Park for automatics).

Step 2: Open Both Bonnets

Locate the batteries. You're looking for two terminals on each battery:

• Positive (+): Usually marked with a + symbol. Often has a red cover.
• Negative (-): Usually marked with a - symbol. Often bare metal or black.

Step 3: Connect the Red Lead (Positive)

Take the red jump lead. Connect one end to the positive terminal (+) of the dead battery. Then connect the other end to the positive terminal (+) of the good battery.

Memory trick: Red to dead first. Then red to good.

Step 4: Connect the Black Lead (Negative)

Take the black jump lead. Connect one end to the negative terminal (-) of the good battery.

Here's the important bit: Don't connect the other end to the dead battery's negative terminal. Instead, connect it to an unpainted metal surface on the dead car's engine block. A bolt or bracket works well.

Why? This grounds the circuit safely. It also means any spark happens away from the battery, not near the flammable gases it produces.

Step 5: Start the Donor Car

Start the working car's engine. Let it run for 2-3 minutes. This allows charge to flow into the dead battery.

Some people gently rev the donor car's engine to around 2000 RPM. This can speed up charging but isn't essential.

Step 6: Try to Start the Dead Car

Turn the key in the dead car. It should start. If it doesn't start straight away, wait another few minutes and try again.

Once the car starts, leave both engines running for a few minutes with the leads still connected.

Step 7: Disconnect the Leads (Reverse Order)

This is crucial. Disconnect the leads in the reverse order you connected them:

1. Black lead from the grounding point (engine block) on the previously dead car
2. Black lead from the good battery
3. Red lead from the good battery
4. Red lead from the previously dead battery

Don't let the clips touch each other or any metal while disconnecting.

Step 8: Keep the Engine Running

Don't turn off your engine straight away! Drive the car for at least 30 minutes. This allows the alternator to recharge the battery properly.

Motorway driving is ideal because the engine runs at higher revs. But any driving helps.

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Quick Reference: Cable Connection Order

Step	What to Do
1	Red lead to dead battery positive (+)
2	Red lead to good battery positive (+)
3	Black lead to good battery negative (-)
4	Black lead to engine block metal on dead car

To disconnect: Reverse the order. Start with step 4 and work backwards to step 1.

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What If the Jump Start Doesn't Work?

Sometimes, the car just won't start. Here's what to check:

• Check the connections: Are the clips making good contact? Wiggle them to ensure a solid connection.
• Wait longer: A very flat battery may need 10-15 minutes of charging before it'll start.
• Check for corrosion: Green or white powder on the terminals can block the connection. Clean it off with a wire brush if you have one.
• Is the battery too old? Batteries typically last 3-5 years. If yours is older, it might be time for a new one.

If the car still won't start, the problem might not be the battery. It could be the starter motor, alternator, or another electrical issue. At this point, it's time to call for professional help.

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What to Do After Jump Starting

You've got the car running. Great! But you're not quite done yet.

Drive for at Least 30 Minutes

This recharges the battery through the alternator. Short trips won't cut it. Aim for continuous driving if possible.

Get the Battery Tested

If your battery went flat for no obvious reason (you didn't leave the lights on), get it tested. Many garages and car parts shops offer free battery tests.

A failing battery will keep letting you down. Better to replace it before it leaves you stranded again. Our car battery care guide explains how to extend your battery's life.

Consider the Cause

Ask yourself why the battery went flat:

• Left the lights on? An honest mistake. It happens.
• Cold weather? Batteries struggle in winter. Keep it charged with regular driving.
• Old battery? If it's over 5 years old, replacement is wise.
• Faulty alternator? If the battery keeps dying, the alternator might not be charging it properly.

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Portable Jump Starters: The Solo Solution

What if there's no other car around? A portable jump starter is your answer.

These compact devices pack enough power to start your car without needing a donor vehicle. They're about the size of a large smartphone and fit easily in your glovebox.

How to Use a Portable Jump Starter

1. Make sure the device is charged (keep it topped up regularly)
2. Connect the red clamp to the positive battery terminal
3. Connect the black clamp to an unpainted metal surface on the engine
4. Turn on the jump starter
5. Start your car
6. Disconnect in reverse order

Prices range from £30 to £150. We recommend buying one with at least 400 peak amps for petrol cars or 800 peak amps for diesels.

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Common Jump Starting Mistakes to Avoid

Even simple tasks can go wrong. Here are the most common mistakes:

• Connecting leads in the wrong order: This can damage electrical systems or cause sparks.
• Connecting black to dead battery negative: Always use the engine block instead.
• Letting clips touch: This can short circuit and damage both batteries.
• Turning off the engine too soon: The battery needs time to recharge.
• Ignoring the underlying problem: A jump start is a temporary fix. Find out why the battery died.

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When NOT to Jump Start a Car

Sometimes, jump starting isn't the right solution:

• Damaged battery: If you see cracks, leaks, or bulging, don't attempt a jump start. The battery needs replacing.
• Frozen battery: In extreme cold, batteries can freeze if they're discharged. Jump starting a frozen battery can cause it to explode.
• Hybrid or electric vehicles: These have different systems. Check your manual or call a specialist.
• You're unsure: If something doesn't feel right, call for professional help.

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Final Thoughts

Jump starting a car is a skill every driver should have. It's simple once you know the steps. The key is staying safe and following the correct order.

Keep a set of jump leads or a portable jump starter in your boot. You never know when you'll need them. And if you've been having battery trouble, consider getting a full free vehicle check to spot any underlying issues.

Stay safe out there. And remember: red to dead first, black to metal last.

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