After all the cables are connected, it’s important to wait a period of time to allow the voltages of the two batteries to equalize – at least three minutes. Then you can start the car with the good battery and let it run for a minute or two. If the battery is really dead or old, you may need to let the newer car run a little longer.
Only now you can try to start the car with a dead battery. It should boot up fairly quickly – if not, your battery may be too old or dead to charge. Once it’s running, you should let both cars run for about ten minutes to allow the dead battery to recharge. Keep an eye on the jumper cables at this point – if they get hot you should stop both engines immediately and let them cool before removing them.
After both cars have been running for ten minutes, you can remove the cables, but you should turn off both engines first to reduce the risk of damaging the electronics of both cars. Disconnect the wires in the reverse order you attached them, keeping the clips away from each other and the body.
Now the formerly dead battery should have enough charge to start it again. If you can, it’s a good idea to drive for about 15-20 minutes, preferably with freeway trips, to give the battery a bit of a boost.
If you’re using a booster pack, it’s an easier process. Just follow the instructions that come with the package – this usually involves connecting the cables to the correct terminals on the battery and turning on the device.
What about hitting a car?
Bump starting is a way to start your car when you don’t have jumper cables on hand. This involves having someone behind the wheel with the clutch pedal depressed while the car is in second gear while one or two people push the car.
Once the car reaches a certain speed, the driver releases the clutch pedal, which causes the engine to rev and the car to start.
This procedure is not recommended for modern cars as it can cause problems with the engine management system and, if the car does not start immediately, can also reduce the life of your car’s catalytic converter.
Also, if your battery is low, the kick start may not work. In other words, better start the car if you can and call professional help if that doesn’t work.
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https://www.telegraph.co.uk/cars/advice/how-to-jump-start-your-car-battery-cables-uk-2021/ How to jump-start a car battery in the UK using cables