You might have heard this before: “If your car battery is dead, just drive around for a bit, and the alternator will recharge it.” It sounds reasonable, right? Unfortunately, this common belief is largely incorrect and can leave you stranded.
Driving to Charge Your Car Battery: The Truth Revealed
So, how long does it actually take to charge a car battery by driving? In reality, it can take several hours of highway driving – typically four to eight hours – to significantly recharge a car battery. Even then, driving alone will rarely bring your battery back to a full 100% charge.
You might have encountered the advice to “drive for 30 minutes after jumping your car to recharge the battery.” This myth has been around for a long time, possibly stemming from older car models of the 1950s. But is it still valid for today’s vehicles?
To get to the bottom of this, we consulted Jeff Barron, an auto electronics expert at Interstate Batteries. Jeff, who manages quality at Interstate and leads ProClinic® seminars for automotive professionals, has decades of experience with batteries and cars.
His expert opinion might surprise you.
“You would need to drive for a considerable amount of time to charge a car battery adequately. It’s crucial to understand that your alternator is not primarily designed as a battery charger,” Barron explains. “It’s simply not realistic to expect your battery to reach a full charge, or even close to it, just from driving.”
Why Your Alternator Isn’t a Dedicated Battery Charger
The common misconception is that the alternator is solely responsible for charging the battery. While it does contribute to charging, its main job is to power your car’s electrical systems while the engine is running. Think about everything that relies on electricity in your modern car: air conditioning, headlights, power windows, infotainment system, and numerous sophisticated computer modules that control everything from the engine and transmission to safety features and sensors.
Protect Your Car Battery with a Smart Charger
For efficient and effective battery charging, consider using a dedicated battery charger like the Interstate® Guardian™ 4. Unlike your alternator, this 4-amp smart charger is specifically designed to recharge your car battery quickly and safely. It offers charging options for various battery types, including AGM, EFB, and lithium-polymer batteries.
Barron clarifies that the myth of charging while driving has a grain of truth. Yes, driving does contribute to charging, and yes, the alternator is involved. However, this charging is most effective at highway speeds. At lower speeds or when idling, the alternator is mostly occupied powering the car’s essential electrical systems. Only when the engine reaches around 1,000 rpm or higher does the alternator have enough surplus energy to send a meaningful charge to the battery – maybe just an amp or two.
Furthermore, it’s important to remember that charging a car battery properly takes time. Dedicated battery chargers, designed specifically for this purpose, typically require 10 to 24 hours to fully charge a car battery, even the “fast” smart chargers. Trickle chargers, which charge at a much slower rate, can take three days or more to achieve a full charge. This slow and steady charging is actually beneficial for battery health, preventing overheating and potential damage that can occur with rapid charging. Your car’s electrical system is designed to manage the charging voltage and amperage to protect the battery.
Barron raises a critical point: If your car needed a jump-start, it might indicate a battery that is already significantly weakened or a more serious underlying mechanical problem. If the battery is the issue, driving alone might not be enough to revive it.
“If a battery is so discharged that it can’t start the car, it’s likely already suffered some degree of permanent damage,” Barron cautions. “While there’s a chance you caught it just as it ran down, if it’s been weak for a while, it has likely lost its ability to hold a full charge. In such cases, you should consider getting a new battery.”
Idling vs. Driving: Which Charges Your Battery Better?
Can you charge a car battery while idling? The answer is a resounding no, or at best, minimally. Charging a car battery by idling could literally take days. If your car required a jump-start, idling will likely not provide any significant benefit, and might even worsen the situation if the underlying problem is not the battery itself.
Get a Jump-Starter for Emergencies
For peace of mind and reliable jump-starting capability, consider keeping a handheld jump-starter in your car, such as those offered by Interstate Batteries. These portable devices can not only jump-start your car but also often include features like phone charging and a built-in light, making them a versatile emergency tool.
FIND A LOCATION
When your car is parked and idling, the engine rpm is too low for the alternator to generate surplus power for battery charging. The alternator is primarily focused on running the car’s essential electronics. Only at higher engine speeds, like those experienced during highway driving, does the alternator produce enough excess amperage to effectively charge the battery.
In fact, prolonged idling after jump-starting your car can actually deplete the battery further. Starting the engine consumes a significant amount of battery power, and if you only idle afterward, the alternator might not even replenish the energy used for starting, let alone add to the overall charge.
How Far Do You Need to Drive to Charge a Car Battery?
So, you’ve jump-started your car and are determined to charge the battery by driving. You understand that highway speeds are necessary for effective charging. But how far do you actually need to drive to make a difference?
The short answer is: a considerable distance.
As mentioned earlier, plug-in battery chargers typically take 10-24 hours to fully charge a car battery. Let’s assume your battery is at around 50% charge (a likely scenario if it failed to start your car).
In this case, it could take approximately eight hours of continuous highway driving to bring your car battery to a near-full charge – perhaps around 75% to 80%.
To put that distance into perspective, eight hours at 65 mph translates to roughly 520 miles. That’s about the driving distance from New York City to Columbus, Ohio!
Even after this long drive, your battery might not reach a true 100% charge. This is because 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 computer systems. Therefore, the alternator is designed to stop charging just before reaching a full charge to protect your vehicle’s electronics.
Tips to Maximize Battery Charging While Driving
How can you charge your car battery faster while driving? To optimize charging efficiency, focus on conserving electrical power within your car and maintaining a consistent engine rpm.
The estimated eight-hour charging time assumes a constant speed of 65 mph. To maximize charging, aim for consistent highway speeds and minimize fluctuations in engine rpm. Hills, curves, and gear changes can divert engine power away from the alternator. Choose a straight, relatively flat route and maintain a steady speed as much as possible. Even brief slowdowns due to traffic can extend the overall charging time.
Conserving electrical power is also crucial. Reduce the load on the alternator by turning off any non-essential electrical accessories:
- Drive without air conditioning or heating (if weather permits).
- Turn off headlights only if it is absolutely safe to do so.
- Dim the brightness of touchscreen displays.
- Unplug phone chargers and other USB devices.
- Turn off the radio and other audio systems.
- Reduce dashboard light brightness.
By minimizing the electrical draw from these systems, you redirect more of the alternator’s output towards charging your car battery. However, remember that many hidden electronics within your car also draw power, so even with these measures, driving for hours remains an inefficient way to fully charge your battery.
The Smart Solution: Battery Testing and Replacement
Ultimately, relying solely on driving to charge a car battery is neither efficient nor the most cost-effective solution.
Instead of embarking on long drives, visit a reputable repair shop or auto parts store and request a professional battery test. This test will provide a comprehensive assessment of your battery’s health, indicating not just its current charge level but also its overall capacity and remaining lifespan. This valuable information will help you determine if your battery is still in good condition or if it’s nearing the end of its life.
Get Your Battery Tested
Before assuming you need a new battery, get it tested at an Interstate All Battery Center® or any location where Interstate® batteries are sold. A battery test will give you a clear understanding of your battery’s condition and help you make informed decisions about charging or replacement.
FIND A LOCATION
Don’t fall for the “30-minute drive” myth. Scientific evidence simply doesn’t support it. Those who perpetuate this myth are only telling half the story.
Trust the experts: For reliable car battery charging and maintenance, dedicated battery chargers and professional battery testing are far more effective than relying on driving alone. If your battery is weak, consider replacing it proactively to avoid future breakdowns and ensure your vehicle starts reliably when you need it to.
