How Long Does It Take To Charge a Car Battery?

You go out to your car in the morning to leave for work and see that your door is slightly ajar, which means that the dome light was on all night. You try valiantly to start the car, but when you turn the key nothing happens – the battery is dead. 

If you’ve ever experienced this dread, you already know that the battery will need to be charged. The time of charging depends on many things, including how long it’s been since the battery was fully charged, the size of the battery, the overall health of the battery and charging system, and the type of charger you have. 

Regardless, you’ll need another way to get to work or you will almost certainly be late. 

How Does a Vehicle’s Charging System Work?


Vehicles use a clever system of parts to maintain the ability to start when driven regularly. 

The battery holds the reserve of energy that supplies the initial burst of power so that the vehicle can start. 

To replenish this power when it’s used, the alternator uses a moving belt attached to the engine’s crankshaft called a serpentine belt. This belt spins a pulley on the alternator to generate electricity. This power is also used to power the vehicle as it drives and uses accessories such as the air conditioning, radio, and headlights.

Since too much electricity can harm the vehicle and the battery, the voltage regulator controls the voltage of the current and makes sure the battery stays fully charged when the vehicle is running.

Electricity Basics

It’s helpful to understand these relevant words that should be found in the battery section of your vehicle’s manual or on a battery or charger that you may be looking to purchase. 

Voltage (“volts”) is like the water pressure in a pipe, while the current (“amps”) is like the flow rate and resistance (“ohms”) is like the pipe size. Electrical power (“watts”) is equivalent to the voltage multiplied by the current, so if you increase either or both of those the wattage increases.

Why Does the Battery Need to Be Charged?

car battery light is on

There are several reasons why the battery could be drained, some easier to address than others.

1) Accessories Left On

In the above example, we accidentally left the dome light on for too long and the battery energy that was powering it was depleted, so there was insufficient power left to start the engine.

Other accessories that will drain the battery are the air conditioning, headlights, radio, and USB charging ports. If the vehicle is off, it’s very important to limit the amount these are used so that the vehicle can be started again.

2) Bad Alternator

Since the alternator replenishes the battery, if it’s not working well the battery won’t charge as it should while it’s being driven.

3) Old or Defective Battery

A battery must be able to hold a charge for a reasonable amount of time. After several years, parts will wear out and it won’t work as well if at all. Corrosion on the terminals or other things that can damage the internal parts of the battery will also decrease the effectiveness of the battery.

4) Vehicle Hasn’t Been Used in Awhile

Even healthy batteries slowly drain, so if the car won’t be driven for more than a week or so it’s a good idea to consider charging it while it sits to ensure that the battery is full enough when you need it. Some vehicles are able to sit longer than others. 

Types of Chargers

car battery charger

There are several types of chargers, so it’s important to choose the one best for your situation. Since the amperage can be thought of as the flow rate of the electricity, higher amp chargers will charge the vehicle faster than lower amp chargers will. 

Lower Amp

These chargers supply a lower amperage (2 amps or 4 amps) so they can take up to a day or two to fully charge the vehicle. They usually supply a continuous stream of power (known as linear chargers). A lower flow rate is better for the battery and may reduce the damage if it’s connected to the car for too long after the battery is fully charged.

A trickle charger is a subset that uses very low amps to maintain a battery that isn’t being used for long periods of time. This may be a good option to maintain RV or motorcycle batteries when the vehicles are only used in good weather, for example. Mechanics may use trickle chargers to maintain the battery while working on the vehicles. 

Trickle chargers aren’t meant to recharge a dead battery but can still usually do so in 1 to 2 days

Higher Amp

High amperage chargers, such as 40 amps, usually replenish a depleted battery in under an hour. 

Linear higher amp chargers are seldom used for vehicles as it’s very easy to overcharge the battery and damage components, but they may be useful to quickly charge something like an electric wheelchair. If a battery is left charging once it’s full, it can be damaged by overheating. 

Multi-stage chargers, also known as smart chargers, use bursts of power instead of a continuous stream to replenish batteries. These are safest and best for the battery health as they turn off automatically when the battery is full. A reliable automotive battery charger is a “must-have” for most car owners and the smart charger type is your best bet.

10 amps is a common flow rate for multi-stage chargers and usually charges a half-discharged battery in 2-7 hours.  

Jump Starting

dead car battery

Jump starting uses an external jolt of electricity to provide your vehicle with the boost it needs to start the vehicle if the battery can’t do its job. This can be done via traditional jumper cables or a jump starter. 

A jump starter is a portable battery that contains all the power needed for the boost, so you don’t need another vehicle. This option is the safest as modern jump starters are nearly foolproof and the cables won’t go on the wrong terminals.

Jumper cables attach to the dead battery at one end and at the other end to a working vehicle’s battery. It’s very important to attach these correctly before starting the working car, as if they are placed on the wrong terminals the entire electrical system can be fried. 

Jumping a car places strain on the alternator, so don’t do it often. Only use it to get home or to a mechanic for repair. If the vehicle needs frequent jump starting it probably needs a new battery or other charging system component. Similarly, if the jumping doesn’t work even though it’s done correctly, the alternator or other part may be damaged.

How Long Does It Take to Charge a Car Battery WHILE DRIVING?

driving problem

The alternator charges the battery while the car runs, so you can try charging the battery this way if you don’t have access to a charger as long as the car can be started. The length of time that it takes depends on several things but is usually between 15 and 60 minutes.

Of course, if the battery is fully depleted it will take longer to charge than one that is less drained. The vehicle may not even be able to fully charge the vehicle just by driving it if the battery was completely empty, but at least you can drive it enough to get to a charger. 

The overall health of the battery also affects how quickly it charges. The car usage cycle is a factor since if the vehicle runs regularly, the battery usually charges faster and lasts longer than one in a vehicle that is driven only occasionally. Older batteries may have a difficult time replenishing the charge. 

Different vehicles also have different battery sizes and charging capabilities so that may also affect how long it takes. 

Since the rotation of the engine (measured as RPM – revolutions per minute) directly relates to the voltage put out by the alternator, it’s a good idea to keep the vehicle at a higher RPM while trying to charge (and definitely over 1,000 RPM). 

Remember that due to gearing, faster doesn’t always mean higher RPM. If your vehicle doesn’t have a tachometer on the dashboard listen for the engine to sound a bit higher-pitched and try to keep it there, though automatic transmissions will often shift down when possible to lower the RPM, so these vehicles may require highway speeds for the best charging capacity. 

While driving to recharge the battery, keep all unnecessary accessories such as the radio off so that as much of the power as possible that is generated by the alternator can go directly to the battery. 

How to Extend the Life of Your Car Battery

how to extend life of car battery

To try to limit the hassle and potential damage from battery charging, practice the following steps to extend the battery’s lifespan. Keep in mind though that batteries need regular replacement regardless of how well they are cared for.

1) Drive!

Longer trips (at least 30 minutes at once) at least weekly are important to allow the battery to fully charge. This prevents damage to the battery that is caused by sulfation. 

2) Secure the Battery 

If the battery is loose in its housing, it may clank around while the vehicle is driving. The resulting vibrations can damage the internal components of the battery, so make sure all the bolts are tightened and the battery is positioned well.

3) Battery Maintenance

Most batteries don’t need much care other than a biannual “checkup” to make sure the terminals are clear of corrosion and external debris is removed. Keep the battery clean and dry for optimal function. Some batteries may need their electrolyte solution refilled, so check this. If you need help, a mechanic, car battery shop, or some auto parts stores can show you how to check this yourself.

4) Don’t Allow Battery to Go Dead

A completely dead battery is tough on the battery and will shorten its lifespan, so try to drive the vehicle regularly or keep a trickle charger on it. 

5) Choose Low Amp Charging

If the battery needs to be charged, choose a lower amperage when possible as it’s better for the battery. Multi-stage chargers are gentle on batteries. 

6) Stop Charging When Full

Overcharging can harm the battery so make sure you use a smart charger or pay very close attention when charging.


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