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Jump start a flat battery

How to use jump leads

Jump leads are a handy way of recharging a flat battery, but they can cause real damage to both cars and people if they’re not used properly. For your safety, and our peace of mind, we’d always prefer you to give us a call and leave the recharging to our experienced technician.

Broken down? Call us on 0800 88 77 66 or request help via the AA app 

If you’re determined to do it yourself, make sure you read the instructions in your handbook and follow those if they’re different to our guidelines below.

Important safety information

  • Batteries produce flammable gases, so:

    • never try to jump start a battery that looks damaged or is leaking
    • don’t use jump leads that are damaged
    • stop using the jump leads if they get hot. Switch off both engines and allow the leads to cool to avoid a possible fire
    • never smoke or allow naked flames anywhere near either battery
    • don’t let any metal objects come in contact with the cars’ batteries, as these could cause a spark and possibly make the battery explode. That includes rings, necklaces, watch straps, hand tools, clips, stray wires etc
  • Don't remove the jump leads while the cars’ engines are running. This can cause serious damage to the cars’ electronics
  • Before you start, remove any loose-fitting clothing – like a scarf or tie – as these could get caught up in the moving engine parts

A step-by-step guide

  1. Find someone with a car who’s happy to help. Their car must have a fully charged battery with the same voltage as yours (usually 12 volts)
  2. Park both cars so their batteries are within easy reach of one another (without the cars actually touching). Keep the handbrakes on and the ignitions off
  3. Use the red jump lead to connect the working battery’s positive (+) terminal to the flat battery’s positive (+) terminal
  4. Take the black jump lead and attach it to the negative (-) terminal on the working battery. Then attach the other end to an earthing point (unpainted metal on the engine block or chassis) well away from the flat battery and fuel system
  5. Keep both engines off and wait for three minutes, then start the working car’s engine and let it run for a minute
  6. Start your car
  7. Leave both cars to idle, at a fast pace, for around 10 minutes
  8. Turn off both cars’ engines and carefully disconnect the leads in the reverse order to the way they were connected (i.e. remove the black lead from your car first and finish with the red lead from the other car). Make sure the leads don’t touch one another, or either car, as you remove them
  9. Restart your car
  10. If your car won’t start there’s probably a more serious problem requiring professional help

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