Can the Battery Be Charged While the Car is Idling?
3 Answers
It is possible to charge the battery while the car is idling, but the charging amount is relatively small, the charging time is long, and the charge may not be stable. Generally, this method is not recommended. Idling refers to the engine running in neutral gear without the car moving, consuming fuel while stationary. The charging duration can also be affected by other factors, such as whether high-power devices are in use inside the car, air conditioning is turned on, or external USB power is being supplied—all of which can increase charging time. Charging while idling consumes more fuel, and emissions during idling are highly polluting. Occupants should not sleep in a closed car with the air conditioning on, as incomplete combustion in the engine can produce carbon monoxide, which can accumulate to lethal concentrations inside the vehicle. If possible, it is advisable to use a dedicated battery charger for charging the car battery.
When the car is idling, the engine is indeed running, and the alternator starts working to charge the battery, but the efficiency is low. The reason is that the idle speed is low, resulting in a smaller power generation capacity, which can only slowly replenish the battery. If the battery is already nearly depleted, relying solely on idling may take several hours to fully charge, far less efficient than driving at higher speeds where the alternator output is much higher. With years of driving experience, I occasionally use idling to charge a weak battery as an emergency measure, but I don’t recommend doing this long-term because idling consumes fuel while providing minimal benefits. During checks, observe whether the charging indicator light on the dashboard is on to confirm the alternator is functioning properly. Regular battery maintenance can help reduce these issues.
My car often sits unused for several days, and the battery runs low. While idling after starting can charge the battery, the effect is really slow. The engine generates little electricity at idle speed, charging like a tiny trickle, taking quite some time to replenish. I usually idle for 10-15 minutes, then drive around for a bit, which charges faster and saves fuel. If the battery is in good condition, idling to charge is fine, but with an older or weaker battery, it's important not to rely on it too much. Regular maintenance to avoid over-discharging the battery is crucial.
