Essential guide to jump-starting a modern car

PUBLISHED: 16:27 10 March 2016 | UPDATED: 16:28 10 March 2016

Cobra JumPack (jump-start, breakdown, battery, charger)

Cobra JumPack (jump-start, breakdown, battery, charger)


The complex electronics in modern cars mean that you can’t simply jump-start them without a second thought. Here’s what you need to know.

A flat battery is almost guaranteed to strike when you’re in a hurry, running late or the rain is beating down. The temptation to simply hook up the battery to another car with a set of jump leads is great, but modern cars jam-packed with electronics often require more care than just connecting a couple of cables between your car and any old other. But this needs more thought than just hooking up the leads.

Capacity and Cables

First off, you need to be sure the flat battery and booster battery are of the same capacity and you must read any instructions on both batteries. Always keep the jump leads clear of any moving or mechanical components in the engine bays and the two cars must not touch each other.

To connect jump leads, start by connecting the red lead to the positive terminal from the booster battery and then attach it to the positive terminal on the flat battery. The black negative lead then runs from the charged battery’s negative terminal and is attached to either the other car’s metal body or part of the engine. DO NOT connect it to the flat battery’s negative terminal as sparks may ignite hydrogen gas from the flattened battery. Once this is all done, start the stricken car.

Accessories Off

Once the car with a flat battery has been started, turn on all of the lights, wipers, heater and anything else that uses electricity. This helps reduce an electrical ‘spike’ when the jump leads are disconnected. Removing the jump leads is the reverse process of attaching them (so black first this time), again being careful to avoid any moving parts of the engine.

Warranty Worries

This method of jump starting applies to most cars, but you need to read the owner’s manual before attempting any jump start as some cars simply cannot be jump started. Many modern cars’ electric are susceptible to significant variations in electrical supply, such as when being jump started, and it can render them damaged or useless. Not good, and it’ll void your warranty.

If your car shows any warning lights on the dash after being jump started, there’s a good chance an electrical component has been damaged or sensed a change in electricity supply. This will require the car being checked by a mechanic. The worst case scenario is the engine’s ECU ‘brain’ is damaged and leaves the car undriveable.

Surge Protection

When you are satisfied that jump starting your car is safe, it’s wise to invest in a set of jump leads with built-in surge protection, which acts in a similar way to a fuse to stop too large a current reaching the flat battery and overwhelming electrical components.

If you are at all unsure whether or not it’s safe to jump start your car or you don’t know how to do this safely, take the safe option and call the breakdown service. Flat batteries are the most common call-out for breakdown companies, but fortunately they are also one of the easiest and quickest to remedy to get you back on the road. Just don’t forget to buy a new one if the old one is on its last legs, or you’ll just be back in the same position a few days later.

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