Can a Car Battery Be Charged at Idle Speed When It's Dead?
3 Answers
When a car battery is dead, it can be charged at idle speed, but the charging amount is small, the charging time is long, and the charge is not stable. Idle speed is used to overcome the engine's own operating resistance, maintain engine speed, and make it more convenient for the driver during driving and temporary stops. The functions of a car battery include: 1. Providing power to the car's starter and ignition system; 2. Supplying a stable DC power source to the car's electrical appliances. The maintenance methods for a car battery are: 1. Charge the battery promptly when the ammeter shows insufficient charge; 2. Adjust the electrolyte density according to different regions and seasons; 3. Add distilled water or a special replenishing fluid when the electrolyte is low; 4. The total duration of starting the car should not exceed 5 seconds each time.
Idling can indeed charge the battery a little when it's dead, but the speed is painfully slow. Having repaired cars for over a decade, I've seen too many car owners thinking idling alone can revive a dead battery. In reality, the alternator only runs at about 800 RPM during idle, generating just enough electricity for the ignition system—the charging current for the battery is pitifully small. During normal driving at 2000 RPM, the charging current can reach 15 amps, but at idle it might only be 5 amps. For example, a 60Ah battery that's discharged would take about ten hours to charge at idle, during which you'd need to avoid using the AC and headlights. The most reliable method is either jump-starting the car and then driving at highway speeds for half an hour, or fully charging the battery before reinstalling it. Make it a habit to turn off all electrical devices before parking, and start the car for a twenty-minute drive weekly—this can extend the battery's life by two years.
Last time when my battery was dead and I got a jump start from my neighbor, I specifically asked the 4S shop technician. He said idling to charge the battery is like filling a swimming pool with a small hose—theoretically possible, but practically unbearably slow. The car's alternator is driven by the engine belt, and at idle speed, the RPM is low, generating only one-third of the power compared to full load. Especially nowadays with so many electronic devices in cars, running the AC at idle might even lead to a deficit. It's best to drive around immediately after starting, keeping the RPM above 2000 for about twenty minutes to fully recharge. If the battery is severely aged, this method is only a temporary fix; replacing it with a new one is the real solution. Always remember to turn off the headlights and dashcam before leaving the car, or even the best battery won't last long under such strain.
