Does the car battery charge at idle speed?
2 Answers
Yes, the car battery charges at idle speed, but the power provided is only about 60%. If high-power electrical appliances are used at idle speed, power will be drawn from the main battery. The car alternator is the main power source of the vehicle, and its speed is generally 2.5 to 3 times the engine speed. If the car's idle speed is 800 rpm, a normal alternator can generate a voltage above 12V at around 1000 rpm. As the speed increases, the generated voltage also rises. At around 2000 rpm, the voltage reaches 14 to 15V, which is sufficient to charge the battery without any issues.
When the car is idling, the battery can indeed be charged, but the efficiency is not high. When the engine is running, the alternator also spins, generating electricity to replenish the battery. Idling means the engine speed is very low, such as when you're stopped at a traffic light. At this point, the alternator spins slower, resulting in limited power generation. Charging under these conditions is very slow. If the battery is severely depleted, idling for a long time may not restore much charge. With over 20 years of driving experience, I've encountered several instances of a dead battery. Idling to charge on the roadside can only provide a temporary solution—don't expect a full charge. It's best to avoid prolonged idling in daily use, as it wastes fuel and increases emissions. Once the vehicle starts, you should drive to increase the engine speed, allowing the alternator to charge more efficiently. It's recommended to regularly check the battery's health and not wait until it's completely dead to take action.
