After jump-starting a car with a dead battery, you should ideally run the car for at least 20 to 30 minutes. This allows the alternator to recharge the battery sufficiently. However, if the battery was deeply discharged or is old and weak, it might not fully recharge in this time, and the battery could fail again soon after turning off the car.

If possible, it’s a good idea to drive the car, rather than just let it idle, as this helps the alternator generate more power and recharge the battery more effectively. If the battery continues to lose charge after running the car, it may be necessary to have the battery and charging system checked by a professional.

To restart a car with a dead battery, you’ll typically need a set of jumper cables and another vehicle with a working battery. Here’s a step-by-step guide:

Materials Needed:

• Jumper cables
• A second vehicle with a charged battery

Steps to Restart the Car Battery:

1. Position the Cars:
   • Park the vehicle with the working battery close to the vehicle with the dead battery. Ensure the vehicles are not touching.
2. Turn Off Both Vehicles:
   • Make sure both cars are turned off before connecting the jumper cables.
3. Attach the Jumper Cables:
   • Red Cable to Dead Battery Positive Terminal (+): Connect one end of the red (positive) jumper cable to the positive terminal of the dead battery.
   • Red Cable to Charged Battery Positive Terminal (+): Connect the other end of the red (positive) jumper cable to the positive terminal of the charged battery.
   • Black Cable to Charged Battery Negative Terminal (-): Connect one end of the black (negative) jumper cable to the negative terminal of the charged battery.
   • Black Cable to Metal Ground on Dead Car: Connect the other end of the black (negative) jumper cable to an unpainted metal surface on the engine block or the frame of the car with the dead battery. Do not connect it directly to the negative terminal of the dead battery, as this could cause a spark.
4. Start the Working Car:
   • Start the engine of the car with the working battery. Let it run for a few minutes to build up a charge in the dead battery.
5. Start the Car with the Dead Battery:
   • Attempt to start the car with the dead battery. If it doesn’t start, wait a few more minutes and try again.
6. Remove the Jumper Cables in Reverse Order:
   • Once the car with the dead battery starts, remove the jumper cables in the reverse order:
     • Remove the black cable from the grounded metal surface on the dead car.
     • Remove the black cable from the negative terminal of the charged battery.
     • Remove the red cable from the positive terminal of the charged battery.
     • Remove the red cable from the positive terminal of the dead battery.
7. Keep the Engine Running:
   • Let the engine of the car with the formerly dead battery run for at least 20 to 30 minutes to allow the alternator to recharge the battery.

Tips:

• If the car doesn’t start after several attempts, the battery might be too far gone and may need to be replaced.
• Check the connections to ensure they’re secure and correct if the car doesn’t start.

Safety Precautions:

• Never let the jumper cable clamps touch each other while they’re connected to a battery.
• Always follow the proper order when connecting and disconnecting the jumper cables to avoid sparks or short circuits.