If you buy two cigarette lighter adapter plugs and a length of twin flex cable, connect a plug to each end of the cable, making sure that the side of the cable with the line on it is connected to the centre connection on both plugs, so that the polarity of both is the same, you can now plug one in to your car's cigarette lighter and the other into a car with a good battery. Only do this with the ignition off. Switch your key to acc and this will give you power to low amp items but you won't be able to run your headlights or start the engine. You can put it in a bag in the glove box for future emergencies.
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If you buy two cigarette lighter adapter plugs and a length of twin flex cable, connect a plug to each end of the cable, making sure that the side of the cable with the line on it is connected to the centre connection on both plugs, so that the polarity of both is the same, you can now plug one in to your car's cigarette lighter and the other into a car with a good battery. Only do this with the ignition off. Switch your key to acc and this will give you power to low amp items but you won't be able to run your headlights or start the engine. You can put it in a bag in the glove box for future emergencies.