If Christmas is the season of goodwill, then winter is the season of flat batteries.
Batteries don’t like cold weather and are more heavily used in winter as your car’s heater, demister, headlights and windscreen wipers are in near-constant use.
If you end up with a flat battery one morning, the quickest way to get moving again is usually to find someone who is willing to show a bit of goodwill and give you a jump start.
Jump starting a car with a flat battery is not especially difficult, but it can go wrong and it pays to be prepared.
In my experience, most people don’t carry jump leads. I have given people with flat batteries a jump start several times over the years – and every single time I have had to use my own jump leads!
Don’t try to jump start a battery that is cracked, leaking or appears damaged in any way.
Here’s how to do it:
- Manoeuvre the donor car (with the good battery) so that your jump leads will reach between the two cars’ batteries.
- Switch off the engines of both cars.
- Connect the red jump lead to the positive terminal of the good battery and then to the positive terminal of the flat battery.
- Connect the black lead to the negative terminal of the good battery and then to an earthing point on the engine or chassis of the car with the flat battery – away from the flat battery (this reduces the risk of sparks). Look for some unpainted metal under the bonnet – a bolt or bracket, or a convenient place on the engine block, perhaps.
- Leave the batteries connected for a few minutes for the flat battery to begin to charge.
- Start the engine of the car with the good battery. Raise the revs slightly with the accelerator and then try to start the car with the flat battery.
- Leave both cars running for a few minutes to allow the flat battery to continue to charge.
- The AA recommends that you should stop both engines before disconnecting the jump leads. Leaving the engines running when you disconnect the leads can cause a sudden change in voltage levels in the car’s electronics, which can damage the electronics on some modern cars. This method is safer for your car, but there is a slight risk that the flat battery will still be too flat to start the engine on the jump started car.
- Disconnect the leads in reverse order – black lead first, then the red lead. Make sure you do not allow the ends of the leads to touch while they are still connected – sparks and damage may result.
- Hopefully, that’s it – both cars can now start up and drive away independently.
If you find yourself with a flat battery regularly, then repeated jump starts are not the answer.
You need to fix the underlying problem, which is that your battery is not being properly charged. I’ve written about flat batteries, battery chargers and booster packs here – take a look if you are having problems keeping your car’s battery properly charged.