Can a car charge the battery when idling after starting?
3 Answers
Yes, a car can charge the battery when idling after starting. All vehicles are equipped with a generator that produces electricity as soon as the engine is running. The battery, also known as a storage battery, works by converting chemical energy into electrical energy. Typically, the battery referred to is a lead-acid battery, which mainly uses lead and its oxides as electrodes and sulfuric acid solution as the electrolyte. There are various types of batteries, including lead-acid batteries, nickel-iron batteries, and nickel-cadmium batteries. In a lead-acid battery, the positive electrode is lead dioxide, the negative electrode is lead, and the electrolyte is a dilute sulfuric acid solution. During use, the positive and negative electrodes react with sulfuric acid to form lead sulfate. When the concentration of the sulfuric acid solution drops to a certain level, the battery must be recharged. Using an external power source for charging can restore the electrodes and electrolyte to their original state, allowing the battery to be used again after charging.
I've been driving a taxi for decades and often encounter this issue. When the car is idling with the engine running, the alternator does work and can indeed charge the battery, as the generator is driven by the belt to produce electricity, delivering current to the battery. At around 800 RPM, the charging current is relatively small, usually only a few amps, which is much less efficient compared to charging while driving. If the battery is already depleted, idling to charge it may take a long time to recover, and idling the engine consumes extra fuel, approximately half a liter to one liter per hour. Prolonged idling is also bad for engine cooling and increases the risk of carbon buildup. I suggest not relying on this method; it's better to drive around or take a short trip for faster and more efficient charging. Battery maintenance is key—regularly check the electrolyte level and voltmeter readings.
I had the same question when I got my new car, but later I found out the answer through research. The car can charge the battery even when idling after starting, because the alternator keeps supplying power while the engine is running. At idle speed, the charging is slower due to low RPM and small current, while normal driving provides a stronger charge. For example, when my car battery was drained, idling for half an hour after starting only replenished a tiny bit, and it wasn't cost-effective due to high fuel consumption. Battery aging or malfunction can reduce efficiency. I usually avoid prolonged idling to prevent engine overheating. If the battery is really drained, it's better to use a charger for direct charging or go for a drive.
