How Long Does It Take to Fully Charge a Battery by Idling in Place?
3 Answers
Idling in place to charge the battery takes approximately 20 minutes to fully charge. The precautions are: 1. Check whether the charger is dual-use for 12V and 24V, as a single battery cannot be charged with a 24V charger; 2. For water-added batteries, the cover needs to be opened during charging, while maintenance-free batteries can be charged directly. Car 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. The functions of the car battery are: 1. To provide power for the car's starter and ignition system; 2. To provide a stable DC power source for car electrical appliances.
As someone with years of car repair experience, I can tell you that the time needed to charge a battery at idle mainly depends on the battery's discharge state and the vehicle's alternator output. A typical private car's battery capacity is generally around 40-60Ah, and the alternator can only output 10-20A current at idle. So if the battery is completely drained, it may take 4 to 6 hours or more to fully charge. But this method is highly inefficient because idling consumes fuel and pollutes the environment, and the battery may also overheat and age. I recommend not relying on this method; instead, using a home charger can get the job done in just a few hours. If the battery is only half-discharged, idling for about 2 hours can boost the charge a bit, but it's still more effective to drive the car for a while.
When my car battery died, I tried idling to recharge it but found it ineffective. One winter when the battery was drained, it took a full hour of idling just to barely start the car—much slower than expected. Idle charging depends on battery condition; new batteries may charge faster, while old ones take longer. Plus, idling produces carbon monoxide, which is dangerous in enclosed spaces, and can cause engine carbon buildup. I always tell my friends it's better to use jumper cables or a charger—idling is just a temporary fix, and 30 minutes is enough. Otherwise, it wastes fuel and isn't cost-effective. The key is regular battery maintenance to extend its life and avoid deep discharges.
