How long does it take to charge a car battery while driving?

[JuliaFitz]

Automotive batteries are typically 12V each. When charging such a battery from a completely discharged state, the general charging time is 8 to 10 hours. Precautions for charging car batteries are as follows: 1. Home charging current is 5A: This allows for faster charging, usually completed in 8-10 hours. Since the battery is used to power the car, if the vehicle's charging system is functioning properly, there's no need to waste time charging it separately, as the car will charge the battery while driving. 2. If planning to stop using the vehicle: If you intend to stop using the vehicle for an extended period, such as one month, you can remove the battery and charge it for 5-8 hours. Before charging, pay attention to the battery type: for flooded batteries, check if the electrolyte level is sufficient; for dry batteries, avoid using too high current as it may damage the battery. 3. Do not exceed 1/5 of the battery capacity in charging current: The charging current should not exceed 1/5 of the battery capacity, especially for older batteries, and the charging duration should not be too long. Calculate the charging time proportionally based on capacity - for example, a 50Ah battery charged at 5A would require 10 hours.

[ZacharyDella]

I found that the charging time for a car battery while driving really depends on the situation. For my daily city commute, when traffic is heavy and I only drive for ten minutes, it barely charges the battery at all—it doesn't even replenish a tiny bit. Short trips like half-hour commutes can only charge the battery to around 30%, far from a full charge. To truly replenish the battery, I recommend driving continuously for over an hour, especially at a steady speed on the highway, as the charging efficiency is much higher then. The higher the alternator's RPM, the faster the charging—below 1,500 RPM, it's sluggish. The battery's condition also plays a key role; an old battery with high internal resistance charges very slowly. After I replaced mine with a new one, the charging speed improved noticeably. As an extra tip, too much city driving can easily lead to battery drain, so taking a short highway trip weekly to recharge is a good practice—it also helps prevent premature battery aging. Don’t forget to regularly check the alternator’s output current to ensure it’s around 14V for proper charging—don’t wait until the car won’t start to regret it. Safety first—a drained battery can leave you stranded, which is dangerous. With proper maintenance, a battery’s lifespan can be extended by two years, saving you money and hassle.

[SanDakota]

As someone who enjoys tinkering with cars, I've noticed that charging the battery while driving requires specific analysis of driving conditions. Idle charging after starting the engine is very inefficient and almost ineffective; effective charging only occurs when the engine speed exceeds 2000 RPM, and continuous driving for half an hour can charge the battery to about 50%. However, to fully charge it, you need to drive for at least an hour or even longer, depending on the battery's capacity and health. I've measured voltage changes with a multimeter, and older batteries with higher internal resistance require more time. If the battery is completely dead, relying solely on driving may not fully charge it, and using an external charger is more reliable. I recommend regularly checking wiring contact points for corrosion, as loose connections can affect charging speed. Extending this to urban congested driving, frequent low-speed driving leads to insufficient charging, so it's wise to keep a portable charger on hand just in case. Battery health shouldn't be ignored—deep discharges followed by multiple short trips can worsen the situation. Regular maintenance of the alternator is key, as proper RPM ensures stable charging. Don't hesitate to replace a battery after five or six years to avoid the hassle of breaking down on the road.

[CollinAnn]

I remember when I first learned to drive, my instructor taught me that the engine automatically charges the battery while driving. The longer you drive, the more it charges. Generally, driving for about thirty minutes can replenish some charge, but a full charge requires at least an hour of continuous driving. Short trips where you start the car and drive for just a few minutes are basically ineffective, as the battery doesn’t get charged at all. Simply put, daily city commutes are too short to be sufficient, while weekend highway drives or long trips are great for topping up the battery. An aging battery charges more slowly, whereas a new one charges much faster. Don’t rely solely on driving to charge the battery; regular vehicle inspections offer more peace of mind. For safety reasons, if the battery is low and starting becomes difficult, it’s best to check it in advance to avoid issues. In terms of maintenance, keep the battery clean and avoid moisture, as cold weather in winter makes charging even harder. Reduce the load by minimizing the use of power-consuming devices like air conditioning during daily drives. Healthy driving habits can also help extend the battery’s lifespan.

[SanAaron]

I commute by car in the city, but the charging efficiency is too low for short-distance driving. Driving for just ten minutes barely changes the battery level. To effectively replenish the charge, I find that driving for half an hour can charge it to about 20-30%, but it’s still far from a full charge. To truly top up the battery, it’s best to drive continuously for over an hour—for example, maintaining a steady speed on the highway can charge it to over 80% much faster. The charging speed depends on the engine RPM; idling is slow, and stable charging only occurs above 1,500 RPM. The battery’s condition also affects the time—older batteries take longer to charge. As an additional point, slow charging in heavy traffic can easily lead to battery depletion and premature aging, so it’s recommended to take a long-distance trip monthly to balance it out. If you notice poor charging performance, first check whether the alternator is outputting a normal 14V, or consider buying an external charger as a backup. Battery health is crucial for safety—insufficient charge can make starting the car dangerous. Regular maintenance and voltage checks can prevent issues and extend the battery’s lifespan to a full five or six years. In winter, charging efficiency is even worse due to low temperatures, so you’ll need to drive more to compensate.