Start the good car and let it idle for a few minutes to charge up the dead car's battery, then fire up the dead car. If your problem was a battery issue, it should start.
Start the Working Car:
Start the working vehicle. You can give the engine some gas and then leave it running for a couple of minutes while it charges up your battery.
Caution: Don't attach the negative cable to the negative terminal of the weak battery when jumping a car battery! This common mistake could ignite hydrogen gas directly over the battery. Battery explosions can cause serious injury.
Ensure both vehicles engines are switched off, remove the ignition keys and open their bonnets (or boot if the battery's located there). Attach one end of the red jump lead to the positive terminal on the flat battery.
In order to jump a car, you need to have a companion car relatively close to the battery of the dead car. Put both vehicles in park or neutral, and turn off the ignition in both cars.
Connection directly to the negative terminal of the broken down vehicle is not recommended, as this can cause sparking, which can damage the battery. In the case of old lead-acid batteries, there may even be an escape of battery acid, which could endanger people in the vicinity.
Attach the red jumper cables first. Start by clamping one red cable to the positive side of the battery that won't start. Then attach the other red clamp to the positive side of the working battery. Next, clamp one black cable to the negative side of the working battery.
When disconnecting the cables from the old battery, disconnect the negative first, then the positive. Connect the new battery in the reverse order, positive then negative.”
While hooking up jumper cables may seem easy, there is a specific way it must be done to avoid the risk of causing expensive electrical damage to your car or may even explode your car's battery! Ensure both cars are turned off and that they can reach one another's batteries with ease.
The battery will charge faster if you rev the engine faster. Why? Because the faster the crankshaft turns, the faster it turns the belt that runs the alternator. And the faster the alternator turns, the more electricity it produces to run all the electrical stuff in the car — and recharge the battery.
If the battery is completely dead, it won't have enough power to turn over the engine, even with a jump start. In this case, you'll need to replace the battery to get your car running again. Another reason why a car battery won't jump is because there is a problem with the charging system.
Leaving jumper cables attached too long can lead to overcharging your battery and damaging it, or possible damage to the other car, leading to two dead car batteries instead of one.
How long do I have to leave jumper cables connected? You should leave jumper cables connected for around five minutes at first. If your car still doesn't start after five minutes, it may take longer—up to 30 minutes in extremely cold temperatures.
The answer to this depends on which vehicle has the inaccessible terminal. If you can't access the negative terminal on the dead car, it's not a problem. In fact, when jump starting a vehicle, experts recommend connecting the negative clamp to a metal ground instead of the negative terminal of the dead battery.
What Happens When Negative And Positive Terminals Touch? If a positive cable and a negative cable on a good battery touch each other, a strong electrical current will flow between them. This may cause sparks, damage the wires' insulation, and potentially start a fire.
Connect the positive terminal first. Attach the red (positive) terminal to the positive battery post. Tighten the terminal with a wrench. Repeat the process with the black (negative) terminal.
Don't attach the negative (black) clamp to the negative terminal of the dead battery. It is important to connect the cables in that order, and it is safest to connect the negative (black) clamp as far from the battery as possible, in order to reduce the risk of sparking that could cause a fire or explosion.
Connect Jumper Cables Correctly
Connecting booster cables seems easy enough: red to red, black to black. Many people get away with this method, but the risks are high. Incorrect jumper cable connections can cause fires and explosions, which can lead to injury or damage to your vehicle.
Just remember the following rhyme. (It's a mnemonic, not poetry.) 'Red from the dead, to red on the good. Black from the good, to under the hood.
Once the dead car's engine is running, remove the jumper cables in the opposite order that you put them on: Disconnect the black clamp from the grounded metal section of the dead car.