charging a car battery

How Long Does A Car Battery Take To Charge?

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A dead battery is one of the most common culprits behind a car refusing to start. That’s because your vehicle’s battery provides the engine with the power it needs to run.

When a car battery dies, it almost always happens when you don’t have much time to spare. So how long does a car battery take to charge?

Today’s guide explains the charging time of a car’s battery using different battery chargers and using its engine. It also covers the factors affecting changing time and signs that your vehicle’s battery needs charging.

An auto mechanic uses a multimeter voltmeter to check the voltage level in a car battery.

How Long Does It Take to Charge a Car Battery

Generally, a car battery takes between 10 to 24 hours to charge all the way.

Depending on the size of the vehicle’s battery and the power output of the charger, it can take a lot less time or much longer than that to fully charge your car battery.

The average car battery size ranges from 40 to 65 Ah (ampere-hours), with 48 Ah being the most typical. This number corresponds to the total quantity of Amps the charger has to deliver to the battery to charge it completely.

As such, if you want to figure out how long it’d take your car battery to finish charging, divide your car battery’s size by the charging rate of the charger.

The thing is, different chargers offer different amounts of power. To make the calculations easier for you, the following are the charging times of a 48-Amp car battery using various battery chargers:

Charging car battery with electricity trough jumper cables with copper clamps attached for start engine car

At 2 Amps

To achieve a full charge, a 2-Amp charger would take 24 hours.

At 4 Amps

To give a full charge, a 4-Amp charger would take around 12 hours.

At 6 Amps

To achieve a full charge, a 6-Amp charger would take 8 hours.

At 8 Amps

To deliver a full charge, an 8-Amp charger would take 6 hours

At 10 Amps

To provide a full charge, a 10-Amp charger would take nearly 5 hours.

At 20 Amps

To give a full charge, a 20-Amp charger would take around 2.5 hours.

Be careful before connecting your car battery to a charger at 20 Amps because it may damage the battery if it’s completely out of juice.

At 40 Amps

To provide a full charge, a 40-Amp charger would take a little over 1 hour.

Due to its high power output, charging your car battery at 40 Amps may damage it if it’s dry.

At 50 Amps

To achieve a full charge, a 50-Amp charger would take almost 1 hour.

This type of charger has a higher potential of damaging your car battery if it’s dead, so proceed with caution.

The car battery is charging while it is shaking from voltage

With an Engine

When your battery is running low on juice or fully drained, using a charger isn’t the only method of recharging. You can have your car’s engine charge the battery instead once you jumpstart it.

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This can happen while you’re driving the car as the vehicle recharges itself automatically via the alternator. The question is, how long does a car need to run to charge a drained battery?

The answer heavily depends on the size of your car battery and the size of the car engine. This results in a wide range of power outputs from alternators, starting from 30 Amps up to 150 Amps.

The RPM (revolutions per minute) of your car’s engine also plays a role in the charging time. An alternator that spins faster takes a longer time to finish charging a car battery.

It can take you around 4 to 8 hours of driving at high speed to fully charge your car battery via the alternator. That’s about 520 miles of driving at 65 mph (miles per hour).

This charging period will load up your car battery only up to 75 to 80 percent as alternators stop short of a full charge.

That’s because delivering more charge as you’re driving and charging your car battery demands higher and higher voltage. Such elevated voltages can damage the vehicle’s onboard computers, so the alternator stops charging at a limit as a protective measure.

Car battery light in dashboard warning about problems. Vehicle panel with red indicator electricity icon and symbol. Service or maintenance needed.

Factors That Affect Charging Time of Car Battery

Various factors can affect the charging time of a car’s battery. As mentioned above, these include:

  • The size of the battery
  • The power output of the charger
  • The size of the engine

But these aren’t the only factors, here are a few more aspects that can impact car battery charging time:

State of Charge

This refers to the amount of charge left in the battery. The higher the state of charge, the slower the charging will be as a way to avoid potential damage due to overcharging.

Battery Degeneration 

All car batteries have a lifespan, which means their condition worsens with usage over a certain period. This degeneration not only affects the battery’s ability to hold a charge but also to take up power when charging.

Battery Temperature

When charging, if the battery’s temperature is too high or too low, the charging efficiency can suffer and may lead to damage. It’s best to charge at moderate temperatures ranging between 50 and 86 degrees F.

Electrical Loads

If you’re using other features of your car that use up charge, this will prolong the battery’s charging time. Examples include air conditioning, power windows, headlights, and radio.

What Speed Is Best for Charging a Car Battery?

You may be tempted to use fast charging on your car battery with a high Amp charger, but this can damage the battery and shorten its lifespan.

It’s best to let your car battery charge at a low to moderate rate between 2 and 15 Amps. This will preserve its condition and lifespan.

Wrapping Up

So how long does a car battery take to charge? The answer comes down to the battery size and the charger’s power output.

An average 48 Ah battery will take about 24 hours to fully charge using a 2-Amp charger, and only half that time at 4 Amps.

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