How Long Does It Take To Charge A Car Battery?

Much like a flat tire or burnt-out headlight, occasionally having a dead battery is just part of being a car owner. Thankfully, if you have a charger or a pair of jumper cables, you should be back on the road in no time.

Yet, “jumping” your car’s battery doesn’t mean it’s charged. Shut the engine off too soon, and you may need to jump it again.

How long does it take to charge a car battery?

One way to estimate charging times is to divide the battery’s capacity, measured in ampere-hours (Ah), by the charger’s amp rating, then add 10%. The average 12-volt car battery holds about 50 Ah, while chargers usually replenish two to 10 amps per hour.

The time taken to fully charge an empty car battery should range from 5.5 to 27.5 hours based on these numbers.

Ultimately, charging times depend on the battery’s capacity, how depleted it is, and the type of charger used.

In this comprehensive guide, I will examine each of these factors and get into more details.

What’s The Capacity Of A 12V Car Battery?

A battery’s Ah rating refers to how long it can supply power without a recharge.

Most 12-volt car batteries have an Ah rating between 40 and 65. The average car battery holds about 50 Ah, meaning it’s full at 50 and depleted or “dead” at zero.

Car, truck, and SUV batteries are categorized by group sizes, something you can read more about in another of our guides.

How Long Does It Take To Charge A Car Battery With A Charger? It Depends On The Charger

Standard Charger

Standard chargers range from about one to 40 amps and often cost the least. Simply attach the terminals to the corresponding posts and flip the power switch.

However, you must watch the charge level and turn the charger off once the battery is full. Leaving a standard charger on and attached for too long can cause the battery to overheat and possibly ignite, an issue known as thermal runaway.

Moreover, even if a charger puts out 40 amps per hour, the battery might not be able to receive as much. Battery manufacturers generally advise using 10 amps or less, as charging a battery too fast can also cause overheating.

Smart Charger

Smart chargers offer far more utility than standard options. Instead of worrying about turning the charger off in time or if the battery is overheating, smart chargers handle everything.

These will assess the battery’s charge, select the optimal output, and shut off once complete.

Yes, you’ll spend more on a smart charger initially. But the added features will eventually pay for themselves by extending the life of your car’s battery.

Some vehicles, specifically those with engine start-stop technology, may even require a smart charger. Using a standard charger can cause the battery to overheat, potentially causing damage.

Trickle Charger

Trickle chargers only put out one to two amps per hour, meaning it will take roughly 24 to 48 hours to fully charge a car battery.

But that’s what trickle chargers are for, leaving the charger on overnight or through the day (or longer) without worrying about the battery.

Moreover, trickle chargers can also be set to maintain a battery’s charge by matching its discharge rate. This is why you’ll often find showroom vehicles attached to trickle chargers, so customers can test the features without draining the battery.

You guessed it, the slower charging times of trickle chargers do produce less heat, making them the best choice overall for preserving your car’s battery.

Can You Charge A Car Battery With Jumper Cables?

Yes, you can technically charge a car battery using jumper cables, but this doesn’t mean you should.

Jumper cables are great for getting a dead car started again, but you’re better off using an actual charger for recharging a depleted battery.

The main reason is there’s no consistent way to measure how much current passes through to the dead battery, upping the odds of overloading it.

A better option is to jump the vehicle and then drive it for a while, allowing the alternator to charge the battery.

How Long Does It Take An Alternator To Charge A Car Battery?

Batteries supply the initial spark that begins the combustion process, but after that, the alternator takes over for powering the vehicle.

While the engine is running, the battery will recharge, though exactly how much current flows depends on the RPMs. When idling, less current will flow. In comparison, “revving” the engine will recharge the battery faster.

For the best results, try to keep the RPMs at 2,000 or above, which should generate a sufficient current not just to maintain but slowly charge the battery.

If the alternator is working correctly, your battery should have enough charge that you can turn it off and back on within 30 minutes to an hour.

As for how long it takes to fully charge a car battery with an alternator, a one- to two-hour drive averaging 55 MPH should do the trick.

Learn more about how long it takes to charge a battery while driving in another of our guides.

How Long Does It Really Take To Charge A Car Battery?

If your car’s battery dies but still holds a charge, you should be able to jumpstart it and get back on the road in 10-15 minutes.

However, if you shut the engine off too soon, it may require another jump. Leave it running for at least 30 minutes to be on the safe side.

To fully charge a depleted car battery, a standard charger pushing 20 to 30 amps is the quickest option and should take just two to four hours. Just know that you run the risk of overloading the battery if you try and push too much current.

Smart chargers are the best option for most, as they can charge a dead car battery in about 5.5 to 6.5 hours, don’t require supervision, and won’t cause any harm.

If you need to replace your vehicle’s battery, check out our guide to the best battery brands for 2022, including Optima, Bosch, Duracell, and more.