After the car has been started using jump leads, it is not a good idea to immediately remove the jump leads and turn off the engine. The two cars should remain connected for a few more minutes while they are running, after which the jump leads are removed in the reverse order of their connection. However, the actual recovery of the charge does not occur effectively when idling. The alternator is driven by the engine and supplies current to the electrical system, but at low speeds it produces a limited amount of electricity. This is usually enough for the ignition, fuel injection, dashboard and electric power steering, but not for quickly charging a completely discharged battery.
After powering up, it is recommended to drive the car for about 30 minutes, preferably at a higher speed and without unnecessary load on the electrical system. This gives the alternator better conditions to restore some of the charge needed for the next start. The time is not exactly the same for all cars, it depends on the size of the battery, how much it has been discharged and the electricity consumption after ignition. If the headlights, wipers, air conditioning and a powerful audio system are turned on, the battery may need more time to restore a sufficient charge.
We recall that when applying power, the positive cable is connected to the positive terminals of both batteries, one end of the negative cable is placed on the negative terminal of the donor car, and the other is usually attached to a metal ground point in the engine compartment of the car with a discharged battery or to the negative terminal.
This approach is used because incorrect connection can cause an electric shock and damage the electronic engine control unit. After connecting, wait a few minutes, start the donor car and let its engine run for another minute or two. Then, try starting the car with the discharged battery. If it does not start, wait a few more minutes before trying again. Driving for about 30 minutes may help temporarily restore the charge, but it does not guarantee that the old or damaged battery will work properly. If the car does not start again after a short period of inactivity, the problem may not only be the discharge, but also the battery itself.