To charge a car battery by running the car, the key factors are driving duration and engine speed (RPM). Here is a detailed summary:
- Typical charging time while driving: It generally takes about 4 to 8 hours of continuous highway driving to significantly recharge a car battery that is partially discharged, but it will never reach 100% charge solely from driving because the alternator is designed to maintain charge, not fully recharge a dead battery
- Short drives or idling: Short drives or just idling the engine are ineffective for charging the battery. Idling provides very low alternator output, so it could take days to charge a battery this way, and often the battery will continue to discharge if the engine is not run at higher RPMs
- After jump-starting: If you jump-start a car, it is recommended to keep the engine running for at least 10-15 minutes to allow some charging of the battery
- Effect of speed and RPM: Charging depends more on engine RPM than vehicle speed. Driving at highway speeds (above 55 mph) or maintaining engine RPM above idle (around 1500 RPM or higher) helps the alternator produce enough current to charge the battery efficiently
- Rule of thumb: For a moderately discharged battery, about 20-30 minutes of highway driving can replenish a reasonable amount of charge, but fully charging a deeply discharged battery requires several hours of driving or a dedicated battery charger
- Battery condition matters: If the battery is severely depleted or damaged, driving alone may not restore it, and replacement might be necessary
Summary
Scenario| Recommended Running Time| Notes
---|---|---
After jump-start| 10-15 minutes| To recharge some charge after a jump
Moderate battery recharge| 20-30 minutes of highway driving| Replenishes some
charge but not full
Full recharge by driving| 4-8 hours of continuous highway driving| Battery
won't reach 100%, alternator limits
Idling| Several hours to days (inefficient)| Not recommended for charging
For best results, use a dedicated battery charger if the battery is deeply discharged or if you want a full recharge faster. References:
