You might have heard the old saying, “Just drive it around for a bit, and the battery will recharge.” It sounds like common sense: the battery starts the car, the alternator charges it, so a dead battery just needs a good drive to come back to life, right?
Unfortunately, that logic is completely wrong.
Driving to Charge: How Long Are We Talking?
To actually put a meaningful charge back into a car battery by driving, you’re looking at roughly four to eight hours of driving at highway speeds. And even then, your battery likely won’t reach a full 100% charge.
You’ve probably come across the “drive for 30 minutes after jump-starting your car to recharge the battery” advice. This myth has been around for ages and might have had a sliver of truth way back when cars were simpler.
But does it hold up today?
Jeff Barron, an auto electronics expert at Interstate Batteries, sets the record straight. As Interstate’s lab manager and a long-time expert on batteries and cars, Barron oversees quality control and leads ProClinic® seminars for automotive professionals nationwide.
His answer might surprise you.
“You would need to drive for a very long time to effectively charge a car battery. Your alternator is designed to maintain a charge, not deeply recharge a dead battery,” he explains. “Reaching a full 100% charge from driving alone is simply not realistic.”
Why Your Alternator Isn’t a Dedicated Battery Charger
While it’s true that driving will charge your car battery to some extent, especially at highway speeds, it’s crucial to understand the alternator’s primary role. It’s not solely a battery charger. In fact, it’s constantly powering a vast array of your vehicle’s electrical systems. From your air conditioning and power windows to sophisticated onboard computers managing everything from your transmission to engine sensors, everything draws power from the alternator.
It’s only when your engine reaches around 1,000 RPM that the alternator starts to have enough spare capacity to send a small amount of charge – maybe an amp or two – back to your battery.
And remember, properly charging a car battery is a process that takes time.
Dedicated battery chargers, even the “fast” or “smart” ones, typically need 10-24 hours to fully charge a car battery. Trickle chargers can take days. This slower charging is actually beneficial for battery longevity, preventing overheating and damage that can occur with rapid charging. Your car’s electrical system is designed to manage the voltage and amperage for battery maintenance, not rapid replenishment from a deeply discharged state.
Barron highlights a critical point: if your car needed a jump-start, the battery was likely already significantly depleted. In many cases, a battery that’s too weak to start the engine has already suffered some degree of permanent damage.
“A battery drained so low it can’t start your car is already compromised,” Barron states. “While there’s a slim chance it just happened to run down, if it’s been struggling overnight, it’s lost capacity. At that point, you should be considering a battery replacement.”
However, even under ideal driving conditions, your car’s charging system can’t match the charging efficiency of a dedicated plug-in battery charger.
Driving is certainly better than just letting your car idle if you’re trying to get some charge back into the battery.
Can Idling Charge Your Car Battery? Don’t Count On It.
Trying to charge a car battery by idling your engine is incredibly inefficient, and in most cases, practically useless. It could literally take days to see any meaningful charge. If you’ve just jump-started your car, and you’re hoping idling will revive the battery, you’re likely facing a battery that’s too far gone, or potentially another underlying mechanical issue that idling simply won’t fix.
When your car is parked and idling, the engine RPM is very low. The alternator is primarily focused on powering the vehicle’s essential electrical systems. It’s not generating enough surplus power to effectively charge the battery. In contrast, at highway speeds, the engine works harder, allowing the alternator to produce extra amps that can be directed to the battery.
So, no, idling will not effectively charge your car battery. At best, it might trickle in a few amps, nowhere near the hundreds of amps needed to start your engine in the first place. Repeatedly starting your car and then only idling it will likely lead to further battery drain, not replenishment.
Driving Distance: How Far is Far Enough to Charge?
Let’s say you’ve just jump-started your car and are determined to charge the battery by driving. You understand highway speeds are necessary for the alternator to seriously engage in charging.
But how far do you actually need to drive?
The short answer is: a considerable distance.
Plug-in battery chargers estimate 10-24 hours for a full charge. Let’s assume your battery is at about 50% charge (a common state when a car won’t start).
It could take around eight hours of continuous highway driving to bring that battery up to approximately 75% to 80% charge.
Eight hours at 65 mph translates to roughly 520 miles.
That’s about the driving distance from New York City to Columbus, Ohio.
And even after this marathon drive, your battery is still not fully charged. As a battery charges, it requires progressively higher voltage to increase its charge level. However, excessively high voltages can damage your car’s sensitive onboard electronics. Therefore, the alternator is designed to stop charging short of a full 100% to protect your vehicle’s systems.
How to Maximize Charging While Driving (Though It’s Not Ideal)
If you find yourself in a situation where driving is your only option to charge your car battery, you can take steps to maximize the charging efficiency. The key is to minimize electrical drain and maintain consistent engine RPM.
The eight-hour estimate we discussed assumes a constant speed of 65 mph. Maintaining a steady highway speed is crucial. Variations in speed, hills, and gear changes can divert engine power away from the alternator. Choose a straight, relatively flat route and maintain a consistent speed as much as possible. Even brief slowdowns due to traffic will extend the overall charging time.
Furthermore, reduce your car’s electrical load by turning off any non-essential electronics:
- Avoid using air conditioning or heating.
- Only turn off headlights if it is absolutely safe and legal to do so.
- Dim the brightness of touchscreen displays.
- Unplug phone chargers and other accessories.
- Turn off the radio.
- Reduce dashboard light brightness.
Every amp saved from these systems can be redirected to charging your car battery. However, remember that numerous hidden electrical systems in your car are always drawing power.
Ultimately, relying on driving for hours is neither the most efficient nor the most cost-effective way to charge your car battery.
A much better approach is to visit a reputable repair shop or auto parts store and request a battery test. A professional battery test provides a comprehensive analysis, revealing not just the current charge level but also the overall health and remaining lifespan of your battery. This allows you to proactively replace a failing battery before it leaves you stranded again.
And please, let’s finally put the “30-minute driving charge” myth to rest. Scientific evidence simply doesn’t support it. Anyone who suggests 30 minutes of driving will significantly recharge your car battery is only telling you half the story.
Trust the battery experts on this one.
Charge or Replace? Get Your Battery Checked
After jump-starting a car, there’s always a chance the battery might still be salvageable. To know for sure before opting for a replacement, visit an Interstate All Battery Center® or any location where Interstate® batteries are sold for a quick and accurate battery test. This will give you the information you need to make the best decision for your vehicle.
