Can Revving the Engine in Neutral Charge the Car Battery?
3 Answers
Revving the engine in neutral can charge the car battery. As long as the engine is running, the battery is being charged. It is better to turn off electrical equipment such as the radio and headlights. If the battery is not old, it can be removed for charging. If it has been used for more than two years, it is recommended to replace the battery. The engine, alternator, battery, and electrical loads in a car form an interconnected system. When restarting the engine after it has been turned off, the charging state of the battery must be considered. The battery can be seen as an energy storage device that powers various loads, while the alternator must charge the battery, acting as the energy provider. If the battery's discharge exceeds its charge, the battery will also discharge.
As a veteran driver with over 20 years of experience, I often get asked this question. Revving the engine in neutral can indeed charge the battery a little, because when the engine speed increases, the alternator spins faster and can output more current to charge the battery. I tried this myself when I was younger—like when the battery was low and I pulled over, revved the engine a few times in neutral, and thought it was charging when the battery light on the dashboard went off. But honestly, it's not very efficient. Modern cars have voltage regulators that automatically limit the current once the battery voltage is sufficient, so revving more won't help. The truly efficient way is to drive the car on the road—the natural variation in engine speed charges the battery faster, saves fuel, and is safer. If you constantly rely on this trick to charge the battery, it likely means there's an issue with the battery or alternator, and you should get it checked at a repair shop ASAP. Revving in neutral not only wastes gas but can also cause engine overheating or part wear, which isn't worth it.
I learned this from a mechanic. Revving the engine in neutral can theoretically charge the battery, but it's practically unnecessary. The alternator in a car is driven by the engine, so higher RPMs mean greater current output from the alternator, allowing the battery to charge more. However, modern vehicle electrical systems are smartly designed to maintain charging even at normal idle speeds. Revving in neutral just overloads the alternator briefly before the regulator restores balance. Worse, it wastes fuel and increases emissions. If your battery keeps losing charge, don't rely on this method—check the alternator's voltage regulator or the battery's health instead. For a safer solution, just take the car for a short drive, and the problem will resolve itself.
