Can the Battery Be Charged at Idle Speed?
3 Answers
Yes, the car battery can be charged when the engine is idling. This is because the engine directly drives the alternator via a belt. Once the engine starts, the electricity generated by the alternator undergoes rectification and voltage stabilization before being directly supplied to the car battery. Below is some information about car batteries: 1. Function: It converts chemical energy into electrical energy, serving as a DC power source. It provides a strong starting current to the starter when starting the engine and assists the alternator in supplying power to electrical devices when the alternator is overloaded. 2. Lifespan: The designed lifespan of a battery is 27 months. 3. Types: Nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, lithium-polymer batteries, lead-acid batteries, etc.
I'm a veteran auto mechanic, and car owners often ask if idling can charge the battery. In fact, the alternator does work at idle, but the RPM is too low to generate much power. A standard car alternator requires at least 2000 RPM for full output, while idle is only around 800 RPM, producing a charging current of maybe 5-10 amps. Let me put it this way—if your battery is completely dead, idling for half an hour won’t charge it as fast as jump-starting and driving for ten minutes. The worst part is that prolonged idling to charge can lead to carbon buildup, and the catalytic converter won’t reach optimal temperature, making it more prone to clogging. I’ve seen many ride-hailing drivers lazily idle with the AC on to charge, only to need carbon cleaning at just 20,000 kilometers.
With 15 years of driving experience and having replaced six batteries, I can personally attest that idling doesn't charge the battery effectively. Last time when my battery was drained and couldn't start the car, idling for forty minutes still couldn't get the engine going, and I ended up calling for roadside assistance. The mechanic used a multimeter to test it for me: after a cold start at idle, the charging voltage was only around 12.3 volts, and when the headlights were turned on, the voltage dropped straight to 11 volts. Later, I learned that the alternator needs to maintain 2000 RPM to reach the standard charging voltage of 14 volts. If you have a voltmeter installed and see the voltage below 13 volts, it means the battery is being drained rather than charged.
