Should I carry a jump starter or jump leads?

The difference in one table

How jump leads work, and their catch

Leads link your flat battery to a donor car's battery, so you need that car, its driver, and enough space to park the two batteries close together. Mazda's CX-5 manual sets out the usual order:

1. Move the booster vehicle so its battery is as close as possible to yours, and switch off lights and air conditioning.
2. With the booster engine off, connect the first lead between the two positive terminals.
3. Connect the second lead from the booster's negative terminal to a grounded metal point away from the dead battery, not to the dead battery's negative terminal.
4. Start the booster vehicle, then start yours and let it run for a few minutes.
5. Disconnect the leads in the reverse order.

The same manual warns not to jump-start a frozen battery or one with a low fluid level, to keep sparks and flames away from the battery, to keep leads clear of fans and belts, and to use only a 12 V booster system. Check your own manual, as earth points and procedures vary between cars.

How a jump starter works, and its catch

A jump starter is a battery pack with its own clamps. You connect it to your battery and start the car, with no second vehicle involved. The NOCO GB40 listing describes spark-proof and reverse polarity protection, which reduces the risk of a wrong-way connection. The catch is that it only helps if it is charged when you need it, so it has to be part of a routine. Seehow long a jump starter holds its charge.

Which suits you

• Jump starter: lone drivers, late-night or rural driving, tight parking where a donor car cannot get close, or a car that sits for weeks.
• Jump leads: households with two cars, drivers who would rather not maintain another battery, or as a backup in the boot.
• Neither on a motorway: Highway Code Rule 277 says not to attempt repairs on your vehicle there. Get to safety and call for help.

Common mistakes

• Leaving a jump starter in the boot for months without checking its charge.
• Clamping the final negative lead to the flat battery's terminal when the manual specifies an earth point.
• Buying leads too short to reach between two cars parked nose to nose or side by side.
• Choosing on peak amps alone instead of the engine size the maker lists.
• Ignoring why the battery went flat: a socket that stays live with a charger plugged in is one possibility. See can a car charger drain the battery.

Related pages

• NOCO Boost GB40 review
• NOCO GB40 vs GB70
• Emergency kit essentials
• Best emergency kits

Frequently asked questions

Can I jump-start a car on my own with jump leads?

Only if you have a second vehicle with a healthy battery that you can move next to yours. Leads carry current from a donor battery; they cannot supply any themselves. A jump starter is the option that works with no second car.

Is a 1000A jump starter enough for my car?

Check the engine size the maker quotes rather than the amp figure alone. NOCO lists the GB40 for petrol engines up to 6.0 litres and diesel engines up to 3.0 litres; a diesel above that needs a larger unit. The Simply SM600 leads are listed for engines up to 3500cc.

Where should the last jump lead clamp go?

Follow your car's manual. Mazda's CX-5 manual says to connect the negative lead to a grounded metal point away from the dead battery, not to the dead battery's negative terminal, and to disconnect the leads in reverse order.

Can I jump-start on the hard shoulder?

Highway Code Rule 277, in its additional rules for motorways, says not to attempt repairs on your vehicle. Get yourself to a place of relative safety, away from the vehicle and traffic, and call for help instead.