How long should the engine keep running after jump-starting a dead car battery?

[AaliyahDella]

If the engine is running at a speed above 2,000 RPM, it will take at least 4 hours to fully recharge the battery. If the engine speed is below 2,000 RPM, the required charging time will be even longer. Additionally, charging while driving takes less time compared to idling charging. Methods to restore power to a dead car battery: Pulse repair: The most effective method to eliminate battery sulfation is pulse repair, which uses instantaneous voltage between 60V to 300V. Higher pulse voltage shortens the repair time, while lower pulse voltage prolongs it. Full charge and discharge repair: This method involves fully charging the battery first, then completely discharging it to restore the battery. Solutions for a dead battery that won't start the car: If you encounter a situation where the car won't start due to a dead battery, you can seek help from another driver to charge your car battery through jumper cables. However, be careful during the connection process: connect the battery positive to the power source positive and the battery negative to the power source negative. Avoid incorrect connections to prevent accidents.

[MorganMarie]

When the car battery is weak and the engine starts, the alternator begins to work. It takes time to charge the battery. Generally, it is recommended to let the engine run for at least 20-30 minutes to accumulate enough charge for the next start. This is because the alternator output current is typically around 10-20 amps, and if the battery is completely drained, it needs to be recharged to 70-80% of its capacity to ensure the next successful start. Especially in cold winter weather, the electrochemical reaction slows down, and charging efficiency decreases, so it's best to drive for more than 40 minutes. Older batteries are even more troublesome—I've seen old cars charge at half the speed, so don't be in a hurry to turn off the engine. If you only drive short distances, the battery won’t get fully charged, and it may soon lose power again. In that case, it’s better to drive a bit longer or take a detour before parking.

[McDelilah]

I've encountered this situation with my car. After jump-starting the battery when it was dead, I let it run for half an hour before turning it off. That time in winter with sub-zero temperatures, charging was slow, but after 30 minutes the engine started smoothly when tested. If you only run it for a few minutes before shutting it off, the battery charges less, and you might not be able to start it again the same day or the next day, especially when you're out running errands, which can be a big hassle. Now I'm in the habit of waiting a bit longer, keeping the radio on to monitor that the sound is steady. If the alternator is working properly, half an hour is enough. For short drives like dropping the kids off at school, I extend it to 40 minutes by taking a longer route to charge the battery. Maintaining the battery well saves trouble; don't rush to turn off the engine to save fuel and end up causing more problems.

[VanNoah]

Starting the car with a weak battery and turning it off too early poses a high risk, as it may not start immediately. For safety, wait at least 20 minutes to allow the battery to charge. With years of driving experience, I often see beginners turn off the engine too quickly, leading to awkward roadside stops. The alternator typically charges at a rate of 0.5-1 ampere-hours per minute, while a standard battery has a capacity of around 45 ampere-hours—half-charged is usually enough for a restart. Charging is slower in cold weather, requiring more time. Avoid turning off the engine in unmonitored areas to prevent being stranded. Make it a habit to check that the vehicle's charging system is functioning properly before driving.