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How to jump start a car

A flat battery while miles from home is never fun, but knowing how to jump a car by connecting the faulty battery to a charged one using jump leads will get you back on the road. In principle, every car can provide jump-start assistance. But to a complete novice, there are many questions to be answered – what is the correct order when bridging? Positive or negative to the battery first? Black or red cable? Read on to learn how to jump-start a car using a charged battery in another parked vehicle.

How to stay safe when jump-starting a car

Our first piece of advice is to make sure you have a warning triangle and high-visibility safety vest in the boot. This is actually mandatory in Europe, but carrying safety equipment as a habit is also just good practice. If your car is parked on a busy road or in a blind spot, you can secure the area with the warning triangle and put on the safety vest to keep yourself visible to other road users.

  • Carefully read your car's instruction manual in case there there are any particular things to know about your model before attempting a jump start.

  • Take off any rings or metal jewellery and make sure not to let anything metal touch the battery.

  • Above all, don't take risks – if there is any damage to either of the vehicles, do not attempt a jump start.

  • If you're feeling at all worried, call a roadside assistance service. They will have the expertise and equipment to get you moving again, safely.

Remember that a jumper connection may or may not immediately start a car, depending on how dead the battery is. After the connections are made, you may need to spend at least a couple of minutes with the two hooked up to charge a dead battery enough to be able to restart your engine. This is why using high-vis safety equipment is recommended.

What you should know about jumper cables

First? Jumper cables that are too weak are useless. A jumper cable should comply with DIN standard 72.553 or ISO standard 6722 and be flexible; the insulating material can harden in the cold.

Second, the pole clamps must be completely encased in plastic; only the contact parts in the crocodile clips should be made of metal. Last of all, jump leads should be chosen according to length, quality, and the engine type of your car.

The steps for jump-starting your car

Depending on the age of your vehicle's battery, the outside temperatures, or if you left the headlights on overnight, your battery might go flat. The easiest way to revive it is with the charged battery of another vehicle.

How to jump-start a car

1. Locate the battery

First of all, you will have to open the bonnet of the vehicles to locate the battery in each of them. The battery may be in the boot in some cars. Make sure they are close enough together that the jumper cables will reach without over-stretching.

2. Connect the cables to each of the cars

Both vehicles must be engine-stopped. Then, connect the cables to each of the cars. The polarity must be respected; this is the first rule. So:

  • Connect the red cable to the positive pole of the donor car. Then clamp the other end to the positive pole of the breakdown car battery.

  • Now connect the black cable to the negative pole of the donor car's battery. The other end goes to the ground connection/ground point of the broken-down vehicle or a free metal spot on its engine block.

  • Do not connect the black cable to the battery of the broken-down car – that will lead to flying sparks!

Important: Do not confuse the plus and minus poles. If you mix them up, you risk expensive damage to the vehicle electrics and potentially endanger yourself and those nearby. For safety, the corresponding symbols are cast into the plastic around the poles, and some are also hammered directly into the poles. If the identification is difficult to find or you are unsure of the polarity in the donor or recipient vehicle, don't risk guessing. Check your car manual or call an expert instead.

3. Start the donor car

Start the donor car and leave it idle for several minutes. This will allow it to provide power to your dead battery. Be sure to follow this instruction; otherwise, you could cause the battery to fail completely or damage the donor vehicle.

4. Start your car

Only after several minutes should you try to start your car. Once the engine starts, reduce both vehicles to an idle.

5. Disconnect the cables

Disconnect the cables in reverse order, starting with the two black cables, then the two red cables. Be careful not to drop them on the mechanical parts of the car and make sure that none of them touch.

6. Let the vehicle run

Let the jump-started vehicle run for about twenty minutes. Drive it to speed up the recharge and make it complete if you get the chance – this is generally about 30 minutes at national motorway speed limits. This will also prevent your battery from draining too quickly if you're waiting to fix a recurring problem.

7. Go to a garage as soon as possible

Go to a reputable garage as soon as possible to carry out a complete check of your car's charging circuit. It might have just been 'one of those things', but it could be a sign of something more serious, so it's always better to be safe than sorry.

8. Invest in a battery booster pack

Consider investing in a battery booster pack. Also known as jump packs, these are small enough to be kept in your boot for emergencies and are used in exactly the same way as another vehicle's battery. Some even come with cigarette lighter ports so you can charge your mobile phone. Booster packs need to be recharged after use and at least once every six months to keep them appropriately powered.

Jump starting electric cars

E-vehicles are also equipped with a classic 12-volt starter battery to activate the high-voltage system. Empty or defective starter batteries are therefore also possible in this vehicle category. The jump start basically works the same as any petrol or diesel engine. If the battery and charging system are generally in good condition, half an hour's driving – in normal conditions, not heavy traffic – should be enough to bring it back up to a full charge.

It is important to note that while receiving jump starts is usually allowed for electric cars, donating jump starts can be risky. Caution is therefore required, and the operating instructions are always decisive. In addition, electric vehicles are usually equipped with smaller starter batteries. For this reason, in the worst case, an electric car that tries to donate electricity could damage its battery or the onboard electrical systems.

The difference between jump-starting and trickle charging

Particularly in older or rarely used vehicles, you might need to recharge your battery with a trickle charger before setting out on the road. Unlike a jump pack – which is just meant to get you going again at speed – a trickle charger is designed to slowly recharge a battery and avoid further damage. How you do this is simple:

  • Remove your battery and connect it to the trickle charger, following the manufacturer's instructions for providing power.

  • Leave it to run for a few hours, or overnight if necessary.

  • The trickle charger will have an indicator that will tell you the level of charge in your battery.

  • Once the indicator tells you the battery is ready, you can reconnect it and get back on the road!

How to take care of your battery

When car batteries are not maintained or if they are old, there is a good chance that weakness will be present, particularly during the winter. In addition, if your car is parked outside, it will be at the mercy of the elements. As a result, the battery can drain very quickly. Follow these tips to prolong the lifespan of your car battery:

  • If the weather is cold, try to park in a sheltered area or use a cover to keep out the worst of the inclement conditions.

  • Just like cold weather, hot weather can cause batteries to drain more quickly, so aim to park in shaded areas.

  • Try not to accidentally leave the headlights or radio turned on when parking your car. Over several hours, this can cause a flat battery.

  • Take your car out for a 30-minute drive once a week if you aren't using it very much. This will keep the battery charged.

  • Keep the battery connections nice and clean by wiping them with a cloth now and then to remove grease and grime. This can also improve its functioning.


Even with regular care, a battery will inevitably need to be replaced. If your vehicle's battery is causing constant trouble, it could be that it's just too old. In emergencies, road assistance services can provide jump-start services or, if necessary, replace a faulty battery with a new one on the spot if the old one can no longer be saved. As this can be costly, it's always better to have the equipment you need in the boot – and the knowledge you need to use it – to get you back on the road and on the way to the garage, under your own steam.


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