Can the car battery be charged without driving after starting the engine?
2 Answers
Yes, the car battery can be charged without driving after starting the engine, because when the engine is running, it drives the alternator to generate electricity. As long as the electrical connections are normal, the battery can be charged properly. However, using the car to start without driving for battery charging is relatively inefficient, and the charging time is also quite long. If a battery charger is used for charging, the time will be shorter. Most people do not purchase chargers for home use, but can charge the battery at nearby auto repair shops. If the battery is already depleted and the car cannot start, it is recommended to use another car for jump-start charging.
I recently encountered a similar situation where my car battery was drained after sitting idle for too long. After jump-starting, I let it idle for half an hour, but it still wouldn’t start after shutting off. A mechanic later explained that while the engine can indeed charge the battery via the alternator when running, the charging efficiency is extremely low at idle—especially with the AC or headlights on. The power generated might only cover basic electrical needs, leaving almost no net charge. I once tested it: the charging current at idle was only about one-third of that when driving. Since then, I’ve learned to drive for at least 15 minutes after jump-starting. Higher RPMs make the alternator more effective—20 minutes of driving charges more than an hour of idling. Plus, prolonged idling can cause carbon buildup, which isn’t worth it.
