How long does it take to fully charge the battery when the car is idling?
2 Answers
It takes about 20 minutes of idling to fully charge the car battery. Idling is to overcome the engine's own operating resistance, maintain the engine speed, and make it more convenient for the driver during driving and temporary parking. Precautions for charging the battery while the car is idling include: 1. Check whether the charger is dual-use for 12V and 24V. If there is only one battery, a 24V charger cannot be used; 2. For water-filled batteries, the lid needs to be opened during charging, while maintenance-free batteries can be charged directly. The functions of the car battery include: 1. Providing power to the car's starter and ignition system; 2. Providing a stable DC power supply for the car's electrical appliances.
When you start the car and let it idle to charge the battery, the time required is actually quite uncertain. Based on my experience repairing many vehicles, it entirely depends on the battery's capacity and the current load conditions. For example, a smaller car battery (around 50Ah) that's half-discharged may only receive 20-30 amps from the alternator at idle, requiring 1 to 2 hours to show any improvement—but this method is highly inefficient. If the air conditioning or lights are on, the alternator prioritizes powering those systems, further slowing the battery charging rate. Moreover, prolonged idling is detrimental to the engine, as it increases carbon buildup. I recommend avoiding reliance on idling; instead, drive the car for 15-20 minutes. Higher engine RPMs enable faster charging and better battery health preservation. Always check for oxidized battery terminals and perform regular maintenance to prevent future discharge issues.
