How long does it take to charge a car battery when it's dead?

[OKiara]

When charging a dead car battery using the vehicle's alternator, the car engine needs to maintain a speed above 2000 RPM, and the vehicle must be driven for at least 4 hours. Below is more information about car batteries: 1. Symptoms of a dead car battery: The starter motor won't turn or rotates weakly, making it impossible to start the engine; headlights appear dimmer than usual; the horn produces weak sound or doesn't work at all. 2. If the car engine cannot be started, you can use the battery jump-start method for charging: This involves connecting another vehicle's battery to the dead battery. After power transmission, the engine can be started, and then the internal alternator will charge the battery while the engine is running. The engine needs to idle for about 15-30 minutes to ensure the battery has sufficient charge. 3. Using a battery charger: When bubbles appear in the battery's electrolyte, it indicates full charge. Passenger car batteries typically have a nominal voltage of 12V, but the actual voltage is slightly higher, usually around 13V when unloaded. By measuring the voltage, when the battery reaches 13V, it indicates the battery is fully charged.