Can the Engine Charge the Battery at Idle Speed?

[GrantDella]

Yes, the engine can charge the battery at idle speed. If the charging indicator light is not on when the car is idling, it means the battery is not being charged and is still discharging. Normally, the charging indicator light should be on, indicating that the battery is being charged, although the charging current is very small. When the ignition switch is turned on, the battery supplies excitation current to the generator through the ignition switch, fuse, charging indicator light, and diode, and also provides voltage to the regulator's detection and control section. The battery is an essential part of a car and can be divided into traditional lead-acid batteries and maintenance-free batteries. Since the battery uses lead-calcium alloy for the grid frame, the amount of water decomposition during charging is minimal, and water evaporation is also low. Additionally, the sealed structure of the casing releases very little sulfuric acid gas. Compared to traditional batteries, these batteries have advantages such as not requiring any liquid addition, easy connection to terminal posts, and long power storage duration.

[LylaLee]

Speaking from experience about whether the engine can charge the battery at idle, here's the deal. When the engine is idling, it is indeed running, and the alternator does work to charge the battery since the alternator is driven by the engine. But honestly, the efficiency isn’t great. At low idle speeds, the amount of electricity generated is minimal, and charging is painfully slow. I’ve tried it several times—charging for just half an hour at idle barely increases the battery level. More importantly, prolonged idling for charging is not advisable—it wastes fuel, harms the environment, and can even cause the engine to overheat due to prolonged idling. If you want faster charging, it’s better to drive for a few minutes to raise the RPM, which significantly boosts charging efficiency. Also, a friendly reminder: regularly check your battery’s condition—don’t wait until it’s dead to panic. Using a home charger is a much more convenient and safer option.

[KaiLynn]

Idle charging is feasible; as soon as the engine starts, the generator kicks in to power the battery. However, from my own experience: idle charging takes too much time, especially during winter warm-ups, and the battery only gains a minimal charge. The low efficiency is mainly due to insufficient RPM, resulting in weak power generation; coupled with running the AC or lights, which consumes even more electricity, the charging effect worsens. This not only wastes fuel costs but may also shorten the battery's lifespan. I've learned my lesson now—when facing battery issues, after a brief idle charge for emergencies, I quickly drive around to raise the RPM, making charging much faster. As for routine maintenance, I check the battery health monthly—prevention is better than cure.

[JaydenDella]

When the engine is idling, the generator can indeed charge the battery, but you need to be cautious. Idle charging is slow and inefficient, consuming more fuel while providing little charge. I've tried emergency operations, and it's fine for just a few minutes; prolonged use can damage the car. Regular driving provides a more stable charging method.