Can a car charge the battery when idling after ignition?

2 Answers
VanDaniela
07/25/25 9:12am
When a car is idling after ignition, it can charge the battery. However, the prerequisite is to ensure that all electrical appliances (except the engine operation) are turned off. Generator working principle: 1. Power source: As long as the generator is working, it can charge the battery, and the generator's power source comes from the engine. 2. Power transmission: After the car starts, the engine begins to work, and the engine transmits power to the generator through a belt, which then starts charging the battery. 3. Charging efficiency depends on vehicle conditions: The charging efficiency differs between idling and driving states. When the vehicle is moving, the generator receives more power.
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McElliott
08/11/25 7:12pm
I'm a veteran driver with over 20 years of experience and have encountered this situation. When the car is started and the engine is running, the engine drives the alternator to work, so of course the battery can be charged. However, charging while idling in place is very inefficient because the engine speed is low at idle, the alternator output is weak, and the charging current is small. It might take several hours to charge just a little bit of power. I once tried to charge the battery by idling to warm up the car in winter, but ended up using half a tank of fuel, the charging was still slow, and the engine accumulated more carbon deposits. Doing this long-term is bad for the car, wastes gasoline, and pollutes the environment. It's okay for temporary emergencies, like charging for ten minutes while waiting for someone, but it's better to drive around keeping the RPM above 2000 for faster and more economical charging. Also, check the battery's condition—if it's severely aged, idling to charge might be even less effective.
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