Can the car charge the battery when idling after ignition?

[McJohn]

Prerequisite: All electrical appliances (except the engine operation) must be turned off. The details are as follows: 1. The alternator can only charge the battery when it is working, and the power source of the alternator comes from the engine. After the car is started, the engine begins to work, and it transmits power to the alternator through the belt, thereby starting to charge the battery. It should be noted that the charging efficiency differs between idling and driving states. 2. When driving the car, stepping on the accelerator increases the engine speed, providing more power to the alternator, which in turn increases the alternator's output and the amount of charge to the battery. If the engine is idling, the alternator's speed is slower, and the output power is limited. 3. The alternator does not charge the battery indefinitely. The battery has a sensor; if the sensor detects that the battery is fully charged, it will stop charging the battery.

[LeEleanor]

Leaving the car idling after starting can fully charge the battery. I've driven for many years, and every time the engine runs, the alternator automatically works to supply power and charge the battery—no need for the car to move. Last winter when my car battery aged, I tried idling for fifteen minutes, and the dashboard showed the voltage rising. However, doing this long-term isn't advisable. Idling at low engine RPM results in slow and inefficient charging, wastes gasoline, and may cause carbon buildup. It's recommended only for emergency use for a few minutes, followed by driving a distance or replacing the battery. While charging, check the battery warning light on the dashboard—if it turns off, charging is normal. Avoid idling in confined spaces like garages to prevent carbon monoxide poisoning.

[DelZane]

As a young DIY car enthusiast, I often experiment with these things. When the car is started but not moving, the engine running alone can charge the battery. The alternator spins via the belt to supply power to the battery, so wheel movement isn't necessary at all. I've measured with a multimeter - at idle, the battery voltage rises above 13 volts, definitely charging. But be warned: idling charges too slowly since the engine RPM is low, resulting in weak generation; it's more efficient and fuel-saving to drive a short distance for faster charging. Also, never do this in enclosed spaces due to high carbon monoxide risk. The fundamental solution is regular battery health checks - replace aging batteries promptly to avoid trouble.

[SanDonovan]

With years of driving experience, I know that even if the car doesn't move after starting, the engine running can charge the battery. The alternator directly supplies power to the battery, regardless of whether the car is driven or not. Once, my neighbor's car had a weak battery, and I advised him to let the engine idle for a while, and it indeed charged up. However, don't charge for too long; idling is inefficient for fully charging the battery and wastes fuel, which may lead to engine carbon buildup issues. A safer approach is to charge for a short time, or better yet, drive the car for more efficient charging. Also, check the dashboard indicators to ensure they don't stay lit; address any issues promptly with repairs.