can you charge car battery by revving

[DeLillian]

No, revving the engine does not effectively charge a dead car battery. While it's true that the alternator—the component that charges the battery—spins faster at higher RPMs, a modern alternator is designed to provide sufficient charging current even at idle. The primary issue with a dead battery is that the alternator needs a minimum amount of residual voltage from the battery to "excite" its electromagnetic field and begin generating power. If the battery is completely drained, revving the engine will have no effect.

The belief that revving helps comes from older vehicles with less efficient charging systems. Today, the best way to recharge a healthy battery that is merely low is to drive the car normally for a sustained period (e.g., 30 minutes of highway driving). This allows the alternator to operate efficiently across various loads. Simply revving the engine while stationary puts unnecessary stress on the engine without delivering a meaningful charge.

If your battery is repeatedly dying, the problem is likely not the charging method but the components themselves. Common culprits include an old battery that can no longer hold a charge, a faulty alternator that isn't producing enough voltage, or a "parasitic drain" where an electrical component continues to draw power after the car is off. A proper diagnosis with a multimeter is needed.

The table below illustrates typical alternator output, showing that output increases only marginally once a certain RPM is reached.

Engine RPM	Approximate Alternator Output (Amps)
Idle (600-800 RPM)	40-60 A
1500 RPM	80-100 A
2000 RPM	95-115 A
2500 RPM	100-120 A (Max Output)

For a truly dead battery, the only safe and reliable solution is to use a dedicated battery charger or jump-start the vehicle and then drive it.

[McReid]

I learned this the hard way. My battery died in the driveway, and I thought I could be smart by just revving it for ten minutes after a jump. It started, but died again the next morning. The mechanic told me that when a battery is that flat, the alternator can't really get a grip on it. You need a long, steady drive or a proper trickle charger to get a full, healthy charge back into it. Revving just wastes gas.

[DiAbigail]

Think of the alternator as a water pump. It can only pump water if there's already a little water in the system to prime it. A completely dead battery is like an empty pipe. Revving the engine spins the pump faster, but with nothing to work with, it's useless. You need an external source—a jump—to provide that initial "prime." Once the car is running, normal driving is all that's needed.

[McBarrett]

It's more about sustained energy than a short burst. The alternator needs time to replenish the battery's charge. Revving the engine in park might give a tiny boost, but it's negligible compared to the energy used to start the car. The real solution is driving. The consistent RPMs and longer duration of a 20-30 minute drive allow the charging system to work as intended, safely restoring the battery.

[Roxanne]

Modern cars are packed with electronics that demand a stable voltage. Aggressively revving a cold engine to charge a battery can cause voltage spikes that potentially harm sensitive computer modules. It's an outdated practice. If your battery is dying frequently, the focus should be on diagnosing the root cause—like a bad battery, alternator, or a power drain—rather than relying on a ineffective and potentially risky shortcut.