How Long Does It Take to Fully Charge a Car by Idling?

[StDelaney]

When a car is completely out of power, idling to charge it at 1500 RPM for 20 minutes can allow the starter to start the engine once. Charging at 1500 RPM for half an hour can charge the battery up to 80%, while charging at 1500 RPM for over 60 minutes can generally fully charge the battery. Below are detailed explanations: 1. Detail One: The exact time required depends on the remaining charge of the battery, as well as the battery's performance and ambient temperature. Over time, the battery will begin to age, slowing down the charging speed and gradually becoming unable to hold a full charge. 2. Detail Two: In low temperatures, the charging time will be longer. Avoid leaving the car parked for too long, as this can lead to battery discharge.

[DelDakota]

Oh, I know this all too well. When I was younger, I was always too lazy to drive around and wanted to charge the battery while idling, but it was a waste of effort. Starting the engine and idling can charge the battery via the alternator, but it's extremely slow. Take my old car for example—it had a 50 amp-hour battery capacity, and at half-empty, the alternator output while idling was only about 10 amps. That meant it would take over two hours just to reach half charge. Plus, it wastes fuel and increases carbon buildup, which is bad for the car in the long run. Now I’ve learned better—if the battery is low, I start the car and drive around for 15 minutes on local streets. The charging is much faster and more efficient. The key is not to treat the car like a phone power bank—forcing a charge while idling harms the car and wastes fuel. Regularly checking the battery’s condition and avoiding deep discharges is the real way to go.

[MacTucker]

From a technical perspective, idling to charge the battery is quite inefficient. When the engine is idling, the alternator output is low, typically just a few hundred watts, with an output current around 10 amps. However, smaller batteries require less time - for instance, a compact car's 40Ah battery might take about 15 minutes to gain enough charge (around 20%) for starting, but a full recharge could take three to four hours. Moreover, idling consumes more fuel and creates heavier pollution compared to driving around. A short 10+ km drive would charge the battery faster and more eco-friendly. Personally, I monitor the voltmeter and stop charging once it reaches about 14 volts - no need to wait excessively. Remember, maintaining good driving habits and regular charging system maintenance will extend battery life.

[MaxLee]

Don't always think that idling can quickly charge your car's battery. Prolonged idling is harmful to the environment. It produces more exhaust emissions, pollutes the air, and wastes energy. The charging efficiency is low when idling, and it may take several hours to see any effect if the battery is completely depleted. I recommend idling for no more than 10 minutes to jump-start the car, then immediately drive around. Normal driving can recharge most of the battery in just 10-15 minutes. Make it a habit to check your car's condition to avoid battery aging or leakage. This way, it's both safe and eco-friendly.

[SophieAnn]

As a car owner, I often remind my friends not to do silly things like waiting for the car to charge. Although idling can supply power to the battery, the alternator's output at idle is low, making charging as slow as a snail. If the battery is deeply discharged, it might take over 30 minutes to recharge fully. This not only increases fuel consumption significantly but also harms the engine. The proper method is to start the car and drive around for 10 minutes at high speed—charging efficiency will be excellent. Also, consider your driving habits: avoid frequent short trips and use a smart charger for maintenance. It saves time, hassle, and protects your vehicle.