How Long Does It Take To Charge A Car Battery?

A Car Battery, often known as SLI Battery (Starting, Lighting, and Ignition) is an important part of modern internal combustion engine vehicles. It is responsible for starting your car’s engine, providing power to all the lighting systems, as well as the ignition system of the car. A dead battery or a battery with a low charge is not something you want to start your day with. So, why does a car battery lose its charge? What are the different ways to charge the battery? How long does it take to charge a car battery?

If you are a car owner, then you will face this issue at least once in your ownership. In this guide, we will take a look at some of the essential factors that lead to the discharge of a car battery. After that, we will also see how to charge a car battery.

In the process, we will try to find the answer to the important question “How long does it take to charge a car battery?”.

A Brief Note on Car Battery

Batteries are an integral part of modern automobiles, be they cars, motorcycles, trucks, or buses. One of the important functions of a car battery is to provide the energy to crank the engine.

When you turn the key or push a button to start your car, the battery turns the starter motor, which in turn rotates the flywheel. When you combine this action with the ignition system, the car engine comes to life.

Once the engine starts, the alternator kicks in and provides the necessary power to the different electrical systems of the car. It even charges the car battery.

The most common and popular type of Car Battery is the Flooded Lead Acid Battery. As the name suggests, the cells of the battery are submerged in a liquid electrolyte (a mixture of Sulfuric Acid and Water).

Speaking of cells, a typical car battery has 6 cells and each cell provides a little over 2 Volts. Internally, all these 6 cells are connected in a series combination. So, the total voltage is just over 12V. We will see the voltage of the battery at different states of discharge in the later section.

During the charge and discharge cycle, the water in the electrolyte evaporates gradually. Hence, as a part of car battery maintenance, you have to check the electrolyte level and top-up by adding distilled water (not regular water or tap water).

Nowadays, Maintenance Free SLI Batteries are becoming popular. The main advantage of this type of car battery is you don’t have to keep track of the electrolyte or add distilled water.

The electrodes and electrolytes in Maintenance Free type batteries are different than regular wet lead acid batteries. The electrolyte in Maintenance Free SLI Batteries is either immobilized with gel agents or is trapped in the microporous material of plate separators. Such types of batteries are also known as Absorbed Gel Batteries.

What Factors Contribute to Battery Discharge?

From the previous discussion, it is clear that the main job of a car battery is to start the car engine. While the lighting and ignition systems also consume battery, the cranking of the engine is by far the main consumer of battery power.

But as the car engine starts and the car’s charging system (alternator, rectifier, etc.) comes to life, it recharges the battery and also provides power to other electrical requirements.

If the alternator recharges the battery while the car is running, why does the car battery discharge at all?

There are a couple of reasons for this. Let us see them now. If the car engine is idling, the output power of the alternator won’t be sufficient to address all the electrical needs.

In this case, the battery provides additional power. Instead of charging the battery, the alternator is discharging the battery by taking extra current from it.

Another case is quite interesting. The battery discharges even after you turn off your car engine and ignition. These are some parts such as the key fob radio, clock, memory (main body, engine, or sound settings), etc. that need continuous power to keep their functions intact.

Even though the current draw due to these loads is very less, it will still discharge the battery. And if you don’t start your car for a long time or take the car only for short trips, the alternator cannot put enough charge into the battery. If this pattern continues, then the car battery will drain significantly and you won’t be able to start your car.

What To Do If Car Battery is Completely Dead?

If you are a car owner, then the scenario of a dead car battery is inevitable. The reason for a car battery discharging significantly so that you can’t start the car can be anything.

If you haven’t started the car in a while and left it unattended for some time, then the battery will slowly discharge and becomes dead.

Another possible reason is the age of your car battery. If it is an old battery, then it struggles to hold the charge even for a short time. If there is a problem with the alternator or the charging system of your car, then it cannot recharge the battery.

If you don’t notice this issue, then the battery is responsible for providing all the energy to different electrical components. As it isn’t charging, it will soon be dead.

So, what to do if you find yourself with a completely discharged or dead battery?

There are a couple of things you can do in this situation. The first and obvious solution is to jumpstart your car. If you have another car in your garage (or you can ask a friend or neighbor for help), then you can use that car and its battery to jump-start your car. The procedure is very simple.

Jumpstart Your Car

Almost all modern cars have their batteries in the engine bay. So, position the cars so that they are facing each other. Now, open the hoods and locate the batteries.

Take a pair of jumper cables. Usually, they will be in red and black colors. Connect one end of the red jumper cable using its clamp to your car battery’s positive terminal and connect the other end of this cable to the positive terminal of the second car’s battery.

Now, take the black jumper cable and connect one end to the negative battery terminal of the second car (with a good battery). Don’t connect the other end of the black jumper cable to the negative terminal of the dead battery.

A safe approach is to connect the other black clamp to a grounding metal or a metal part without any paint. Refer to your car owner’s manual for additional information on jumpstarting.

Start the second car and let it run for a couple of minutes. You can now try to start your car. If there are no additional problems, then your car engine should start.

You can now remove the clamps in the exact reverse order. Black clamp on your car, black clamp on the second car, red clamp from the second car, and finally the red clamp from your car.

After jumpstarting your car, you have to let it run for some time or take it for a spin (for a long spin) before shutting off the engine. The alternator will charge the battery at this time.

The second solution, if you have a completely flat battery, is to charge it using an appropriate charger. Before taking a look at charging a car battery with an external charger and also different types of chargers, let us quickly go through the chemistry of a charge and discharge cycle.

Charge – Discharge Cycle of a Car Battery

For this explanation, we will take the flooded lead acid battery as an example. The positive electrode in a lead acid battery is Lead Peroxide (PbO₂) while the negative electrode is lead (Pb). The electrolyte is dilute sulfuric acid (H₂SO₄ + H₂O).

Assume you have a fully charged car battery. When you connect a load across the positive and negative terminals, a chemical reaction in the battery causes the flow of current. In the process, both the positive and negative electrodes gradually become lead sulfate (PbSO₄).

Depending on the level of discharge, both the electrodes completely become lead sulfates, and eventually, the battery has no electric potential. The reverse happens when you charge the battery. At the negative electrode, the excess electrons attract the positive hydrogen ions and they combine with the sulfate to form sulfuric acid.

Electrolyte water splits into Hydrogen and Oxygen ions. These Oxygen ions mix with lead sulfate on the positive electrode and form lead peroxide (or lead dioxide) leaving the electrolyte with sulfate ions.

After the charging action, the battery is once again ready to provide current to a load. An important point to remember here is that while charging a lead acid battery, it releases a small amount of hydrogen gas, which we know is flammable. So, you have to be very careful while charging the battery externally.

Different Methods of Charging a Car Battery

Charging a car battery has the opposite chemical action of discharging. Here are different methods of charging a car battery.

• Constant Current Charge: In this method, we apply a constant current to charge the lead acid batteries. This method is not often used outside experimental or laboratory setups.
• Constant Voltage Charge: This is one of the common methods for charging automobile lead-acid batteries. In this method, we apply a constant voltage with the maximum possible current to charge the battery. As the voltage reaches the peak value (a little over 12V for car batteries), the current drops until it reaches 100% of charge.
• Constant Current – Constant Voltage Charge: This method is quite popular for charging deep-cycle batteries. Initially, a constant current is applied until the battery reaches its peak voltage value. After that, the voltage is maintained at that level and the current drops gradually until it reaches 100% of charge.
• Pulse Charge: In this method, a DC Pulse is applied to the battery for a fixed duration.
• Trickle Charge: It is a type of constant current charge but the current is very low. This method will maintain the battery at a full charge state without overcharging and it also compensates for self-discharge.
• Float Charge: This is another “maintaining” type of charging method. In this, we apply a constant voltage at a low current to maintain the charge of the battery.
• Rapid Charge: Also known as Fast Charge, this method charges the battery for a short duration. This isn’t as effective as regular charging.

How to tell if the battery is fully charged? There are a couple of ways you can determine this. The first and easiest way is to check the open circuit voltage of the battery. Open circuit voltage means we haven’t connected any load to the battery. Just check the voltage across the terminals of the battery with the help of a multimeter.

The following table shows the levels of voltages for a typical lead acid car battery corresponding to the state of its charge.

Another way to determine if the battery is fully charged or not is to check the specific gravity of the electrolyte. The following table shows the specific gravity of the electrolyte of a lead acid battery.

How Long Does It Take to Charge a Car Battery?

We have seen the chemical process of charging a battery and also different methods to charge a car battery. But the important question is “How long does it take to charge a car battery?”. The answer to this depends on several factors such as:

• State of Charge (or depth of discharge)
• The capacity of the battery
• Type of battery
• Age of battery
• Temperature of battery

Let us assume the battery is of type flooded lead acid and is fairly new. Also, the capacity of the battery is 12V 60Ah. If you are charging your car battery using an external charger, the duration it takes to fully charge depends on the depth of discharge (or state of charge) and the charge rate.

The following table shows the list of typical durations it might take to charge a battery corresponding to the charge rate.

These numbers are just for reference and the actual time for charging a car battery will depend on several factors.

Some people wonder if a car battery is dead and we jumpstarted it, can we continue to charge the battery using the jumper cables? Please don’t do this. The purpose of jumper cables is to provide momentary connections between two cars and you shouldn’t use them as charging cables.

Even if it works, it may cause problems with the electronics of both cars. So, we advise against doing this.

The next important question is how long does it take to charge a car battery only using the alternator? To charge your car using an alternator, the engine’s RPM must be high.

So, your car shouldn’t be idling, and start and stop traffic in a city also doesn’t help. The best way to ensure the alternator charges your car battery is to take it on a highway (or motorway) and also other electrical and electronic devices must be off.

Even then, there is no guarantee that this will completely charge the battery. The best solution is to drive the car for 30 to 40 minutes so that alternator puts some juice into the battery and then charges it with a proper battery charger.

The selection of the right battery charger is an interesting topic. So, we would like to cover that in a dedicated guide. But any modern smart charger would do fine.

Conclusion

Car Battery is an important part of the car’s electrical system. It provides the oomph to crank the engine and also helps the ignition system as well as other electrical applications.

With proper care and maintenance, the battery in your car will last a long time and will serve you without any hiccups.

A flat or dead car battery is every car owner’s basic nightmare and they will face this issue at least once in their car ownership. If the battery is good but just went flat, you can simply jumpstart your car and let the car charge the battery.

Alternatively, you can use a good car battery charger to charge the battery and bring it back to life.

In this guide, we saw the basics of car batteries. After that, we also saw the important question “how long does it take to charge a car battery?”.