Revving the engine can help charge a battery faster, but only when the battery is very low or nearly dead. With a healthy battery, revving will not make much difference in charging speed. However, there are some important factors to consider when revving to charge a dead battery.
How Revving Helps Charge a Low Battery
In a normal running engine, the alternator provides sufficient charge to keep the battery topped up. But when the battery is very low, the extra output from revving can provide more current to charge it faster.
Here’s why:
- The alternator turns at engine speed via a belt. So higher revs spin the alternator faster.
- A faster spinning alternator generates more electrical output.
- This allows more current to flow into the battery for faster charging.
So by revving a depleted battery, the increased alternator output can provide a boost of charging current. This is especially useful when jump-starting a dead battery.
How Much and How Long to Rev
When revving to charge a dead battery:
- Keep revs between 1500-2500 rpm. Going much higher risks engine damage.
- Rev for 2-5 minutes maximum. This avoids overheating or oil starvation.
- Once started, drive for at least 30 minutes to continue charging. Avoid turning it off again until the battery is charged.
The aim is to briefly rev to get current flowing into the dead battery. Then drive normally so the normal charging system can fully recharge it.
Cautions When Revving to Charge
While revving can help in some situations, there are some important cautions:
Engine Damage Risk
Revving a cold engine puts extra stress on components before the oil warms up. This can lead to premature engine wear over time.
To minimize this risk:
- Allow the engine to idle for 1-2 minutes before revving, to warm and circulate oil.
- Accelerate gently when revving, with no sudden full throttle.
- Do not rev for more than 2-5 minutes. The battery will not gain much more charge beyond this.
Overheating Risk
Sitting still while revving prevents airflow over radiators/cooling systems. This can lead to rapid overheating.
- Monitor engine temperature gauges when revving.
- Again, limit revving to 2-5 minutes maximum.
Battery Damage Risk
Severely discharged batteries can be damaged by excessive current flow.
- Use a battery/charging system tester if available to check the state of charge first.
- If very low, charge slowly at first before revving.
Overall, revving can help charge a depleted battery faster in some cases. But extended high revving without driving risks engine and battery damage. It’s best as a brief assist to jump-starting, not a standalone charging method.
When Revving Helps Charge the Battery
There are a few scenarios where revving can assist in charging:
Jump Starting a Dead Battery
When jump-starting a dead battery:
- On the donor car, rev gently to 1500-2000 rpm while cranking the engine. The extra output can help start the dead car.
- Once started, rev the dead car to 1500-2500 rpm for 2-5 minutes to get current flowing into the battery.
- Drive for at least 30 minutes to fully charge.
This brief revving “wakes up” the dead battery to accept a charge. Driving then provides full recharge.
Push Starting with Low Battery
If the battery has enough charge to partially crank but not fully start:
- Push or roll start the car to start the engine.
- Then rev gently for a couple of minutes to build some charge.
- Drive normally to continue charging.
Revving helps provide charge to ensure the battery will keep the engine running.
Cold Mornings
On cold mornings, a marginal battery may struggle when it’s cold.
- Try starting without revving first. If it won’t start:
- Rev gently for a minute or two to get current flowing into the battery.
- Then try starting again. The brief charge may help it turn over.
- Drive as normal once running.
The revving provides a bit of warmth and initial charge to help a cold marginal battery. But continue driving to fully charge.
Diagnosing Charging System Issues
If the battery goes dead frequently:
- Revving the engine can reveal certain charging system faults:
- If the battery voltage doesn’t increase with revs, the alternator may be faulty.
- If accessories dim when revving, the alternator belt may be loose or broken.
- If the car runs normally when jumped but dies when disconnecting jumper cables, the alternator is likely bad.
Check for underlying system issues if the battery needs frequent revving charges.
Revving to Warm Up Engine
Revving will make the engine warmer faster by increasing combustion and heat output. But there are better ways to warm an engine:
- Drive gently until normal operating temperature is reached. Avoid high revs.
- Use lighter viscosity oil in colder climates to reduce warmup time.
- Install an engine block heater for easier cold starts if needed.
Driving gently warms all components safely and evenly. Idle/revving creates hot spots that can lead to uneven expansion and wear.
Alternatives to Revving for Charging
While revving can provide a brief charge boost, there are safer charging options:
- Use a smart charger to slowly charge a dead battery. No revving is needed.
- Install a battery maintainer to keep the charge topped up if the vehicle sits unused for long periods.
- Fix any parasitic drains identified from a charging system test, to prevent discharge when parked.
- If the battery is more than 3 years old, simply replace it with a new one. Trying to revive an old battery through revving risks damage.
- Upgrade to a higher capacity battery if the existing one struggles to hold charge.
address revving risks and the root cause of a dead battery, instead of relying on temporary revving Band-Aids.
Frequently Asked Questions
How long should I rev my engine to charge the battery?
You should only rev the engine for 2-5 minutes maximum when trying to charge a very low battery. This brief revving can help “wake up” the battery and get the current flowing. But any more than 5 minutes provides minimal extra charge while risking engine damage. It’s best to then drive for at least 30 minutes to fully charge the battery.
Does revving the engine help a dead battery?
Yes, gently revving the engine can help provide a boost of charge to a dead or nearly dead battery. By spinning the alternator faster, revving allows it to supply more electrical output to charge the low battery. This can help when jump-starting a dead battery, or on cold mornings with a struggling battery. However, extended high revving without driving risks overheating the engine and should be avoided.
What revs are needed to charge a car battery?
When trying to charge a low battery through revving, keep the engine speed between 1500-2500 rpm. This provides additional alternator output without over-revving. Revs lower than 1500 rpm typically won’t generate enough additional current to make a difference. While revs higher than 2500 rpm can risk engine damage without providing much more charging capacity.
Will revving the car in neutral charge the battery?
Yes, revving the engine in neutral can still charge the battery, since the transmission gearing does not affect alternator operation. The alternator turns at engine speed whether in neutral or gear. So revving in neutral spins the alternator faster, producing more electrical output that can help charge a low battery. However, extended high revving in neutral should still be avoided to prevent engine overheating.
Conclusion
Revving the engine when the battery is very low can provide a faster initial charge, especially when jump-starting. This allows driving the vehicle normally to complete recharging the battery.
However, extended high revving without driving risks engine damage from overheating and oil starvation. It can also damage an already depleted battery with excessive current.
Use revving cautiously when truly needed to assist in charging a dead battery. But address any root causes of battery discharge, and use safer charging methods to minimize the need to rev.
