How to Use Jump Leads Safely (Correct Order, Every Time)

Before you connect anything

Park the working car close but not touching. Switch both engines off, remove both keys, and turn off the lights, radio, heater and anything else that draws power. Check both batteries for cracks or leaks — never jump start a visibly damaged, leaking or frozen battery.

Keep the leads well away from belts and fans, and take off any dangling jewellery.

The correct connection order

Follow this sequence exactly:

• Red lead to the positive (+) terminal of the flat battery.
• Other end of the red lead to the positive (+) terminal of the good battery.
• Black lead to the negative (−) terminal of the good battery.
• Other end of the black lead to an unpainted metal earth point on the dead car's engine block — not the flat battery's negative terminal.

Why that last step matters

Charging a battery produces hydrogen gas. Making the final connection away from the battery keeps any spark away from that gas. It is the single most important safety step and the one most often skipped.

Starting up

Start the donor car and let it run for two or three minutes. Then start the flat car. If it does not fire within about ten seconds, stop, wait a minute and try again — continuous cranking overheats the starter.

Once it runs, leave both cars connected and idling for a couple of minutes before disconnecting.

Disconnecting — reverse order

Remove the black lead from the engine block, then the black from the good battery, then the red from the good battery, then the red from the recovered car. Never let the clamps touch each other or any metal while the other end is still attached.

Then drive for at least 20 to 30 minutes at a decent speed, ideally on a road like the A56 or M60 rather than stop-start city traffic, to put some charge back in.

When not to try it yourself

Skip the leads and call for help if the battery is damaged or leaking, if you drive a hybrid or electric car, if the battery is hidden in the boot or under a seat with no obvious jump points, or if you are anywhere near live traffic. A mobile jump pack does the job without a second car and without the guesswork.