Everything You Need To Know About Car Battery Voltage [In-Depth Guide]

A car battery is the ultimate source of power for the electronic gadgets inside a car and for the car itself. Therefore, it is believed to be one of the most important components of any vehicle. If your car’s performance isn’t up to the mark, then a low voltage battery may be the reason for it.

A car battery voltage has to be of a certain level and you need to check it on a regular basis to be prepared in case your battery needs to be replaced. Here is all you need to know about the voltage of your car battery:

What Is the Voltage of a Car Battery?

Batteries can be of various types and most of them have different voltages. The voltages range from 1.5V of AA batteries to the most common ones which are of 12V. While we talk about volts and voltages, majority of people are unaware of the meaning behind these words.

In the case of car batteries, the term “voltage” actually refers to the electric potential difference between the negative and positive posts of a battery. The greater that potential difference is, the higher the voltage reading will be. From this, another important question arises: What is electrical potential?

Electric potential is the charge difference between two distinct points. For car batteries, those points would be the terminals of the battery. While one terminal is negatively charged i.e. there are excessive negatively charged particles or electrons on the post, the other is positively charged, having insufficient or lesser electrons on them.

Both the terminals are separated physically so that the electrons do not get transmitted from the positively charged post to the negatively charged one. Once these two posts are connected through a circuit, those negatively charged particles are free to proceed towards the positive terminal. This movement of electrons is called electric current, and it is measured in amperes (also called amps).

What Should Be the Voltage of a Car Battery? (Car Battery Voltage Range)

Following is the breakdown of the voltages a car should be at during its different stages:

Fully Charged Car Battery Voltage

When a battery is completely charged, its voltage should be at 12.6 volts or above. But this rule is applicable when the engine is turned off. If you measure the voltage of your car battery shortly after you had the engine running, it is likely that you’ll get a higher and wrong reading.

It is essential that you let your car sit idle for a night and measure the “resting voltage” to get an accurate voltage measurement. A voltage at this point that is below 12.6V indicates that either your battery isn’t charged to its full potential or it has malfunctioned.

The Voltage of a Car Battery When You Start Your Car

Every time you start your automobile, its battery becomes the source of power for the starter motor which in result uses that power to turn over the engine. At that time, the voltage of the battery drops for a small amount of time, before going up again.

If the battery of your car is in a healthy condition and doesn’t have any faults, its voltage when you start your car should be 10 volts or higher. Although, extreme weather conditions such as freezing temperatures can also cause the voltage to drop and increase the power requirement of the engine to turn over.

The Voltage of a Car Battery When the Car Is Running

When the engine of your vehicle is running, the voltage of your car battery should be between 13.5 and 14.7 volts. During that time, the alternator of your vehicle is busy charging the battery; therefore a voltage appears that is higher than usual.

In case of higher or lower voltage readings than the ones mentioned above, your battery and alternator might be faulty and not functioning properly.

3 Factors that Can Affect the Voltage of a Car Battery

Although the voltage readings mentioned above are quite accurate and shouldn’t fluctuate much unnecessarily, the following factors can have a huge impact on it:

1. Freezing Temperatures

You might be aware of the fact that it is generally advised not to park cars outdoors in freezing temperatures. There is a reason for that. During cold weathers, the car batteries that are fully functional and charged, their ability to provide the high current required by the starter motor goes down by approximately 40 percent.

Therefore the voltage of your car battery when you start your car may get decreased if you are in colder climates.

2. Aging Battery

When your battery ages to a certain extent, its ability to hold charge slowly decreases with time. This can be a reason for a decreased voltage reading.

3. State of Charge (SoC)

The SoC of any electric battery is its level of charge relative to its capacity. When your battery is being charged and discharged, the voltage will surely keep altering. While calculating the voltage of your battery, it is important that you understand the point where the battery stands at in its charge cycle, as it can greatly affect it.

How to Check the Voltage of a Car Battery

Checking the voltage of a car battery is quite an easy task. You don’t need to hire any professional for the job or spend a bulk of money on it. All you need is a multimeter, a hydrometer, or a power probe to get your answers. Here are three different approaches to check the voltage of your car battery:

Checking the Voltage of Your Car Battery with a Multimeter

• First of all, set your voltmeter to 20 DC volts.
• Connect the negative meter probe (typically black) to the negative battery post (also black).
• Connect the positive meter probe (typically red) with the positive battery post (also red).
• Now call for assistance and ask them to turn on the headlights of your car to provide a light load to your battery.
• Now simply check the reading on your voltmeter.
• The optimum temperature should be around 26°C.

Following are the possible voltage readings and their meanings:

• 12.5V or higher: Your battery has a sufficient charge.
• 12.3V: Your battery is charged about 75%.
• 11.8V or lower: Your car battery is charged about 25% or less.

When a voltmeter shows a low voltage reading, it indicates that the chemical reaction of the battery isn’t up to the mark. To improve the reaction, you need to charge it slowly and check the voltage again. If the reading is still low, then it might be an indication of a dead or faulty battery.

Checking the Voltage of Your Car Battery with a Power Probe

Checking the voltage of your car battery with a power probe is relatively simpler as you don’t need to set it to any specific settings.

• Connect the probe’s negative connective lead (typically black) to the negative battery terminal (also black).
• Connect the probe’s positive connective lead (typically red) to the positive battery terminal (also red).
• Now call for assistance and ask them to turn on the headlights of your car to provide a light load to your battery.
• Now simply check the reading on your power probe.
• The optimum temperature should be around 26°C. Cold temperatures are actually believed to increase the efficiency of power probes.

Following are the possible voltage readings and their meanings:

• 12.5V or higher: Your battery has a sufficient charge.
• 12.3V: Your battery is charged about 75%.
• 11.8V or lower: Your car battery is charged about 25% or less.

Similar to a voltmeter, when a power probe shows a low voltage reading, it is an indication that the chemical reaction of the battery has some problem and needs to be improved. To do so, you need to slow charge the battery and check the voltage again. If the reading remains lower than required, then your battery might be dead or faulty.

Reading this article may help you understating more about this topic!

Why Does the Voltage of a Car Battery Drop Overnight?

The voltage of your car battery can drop overnight because of one of the following reasons:

• The lifespan of your battery has come to an end.
• A parasitic drain is consuming the power of your car battery.
• There is a fault in the electrical system of your car.

Although finding the actual root of the problem is a DIY task, you can consult a professional if you’d like to be entirely sure. Following are some simple approaches you can take to diagnose the actual problem:

1. Visual Inspection of the Battery

Sometimes the battery doesn’t hold any charge because of its poor maintenance. Disconnect your battery from its tray and check for any corrosion, bulges, and if the electrolyte level is sufficient enough. In case of a damaged battery, replace it and your problem will be solved.

2. Performing a Battery Terminal Test

Performing a simple battery terminal test will help you check if the terminals of your battery are making proper contact with the battery posts. With this test, you will get to know the voltage drop between the two.

If the voltage drop is quite high, it indicates that the charging system is not capable of providing enough charging voltage to the battery and, as a result, the battery is unable to provide enough power to the starter motor.

3. Performing Battery Voltage Tests

Battery voltage tests can be performed using a multimeter or a power probe as described in the above section. Perform those two tests to know where your battery and its charge stand exactly.

4. Checking for Battery Leakage

Sometimes battery leakage can be the cause of a voltage drop. If your battery is in great condition and seems to have proper, firm connections, then checking for a battery leakage might be your best option.

All you need to do is set your voltmeter to a low setting on DC volts. Connect the negative meter lead (typically black) to the negative battery terminal (also black). Now touch positive meter lead (typically red) to different areas on the upper portion of the battery. If your voltmeter registers even the smallest of voltage, your car battery is leaking charge.

The battery needs to be cleaned. Move to the next approach to know how.

5. Fixing a Leak

Did you know that you can fix a battery leakage by simply cleaning your car battery?

Take a bowl and mix 1 cup of water with 1 tbsp of baking soda into a paste. Now apply this cleaning mixture on with a soft cloth on the outer layer of your battery. Wipe it with a clean cloth. If your car battery has removable caps, make sure you prevent the mixture from penetrating inside the battery, else it will ruin it. Now repeat the battery leakage test.

6. Performing a Hydrometer Test

Similar to a voltage test, hydrometer test, also known as electrolyte gravity test can let you know the SoC of your battery. Following are some preventive measures you need to take before you start with the process:

• Protect your skin and eyes from the harmful effects of acid by wearing acid-resistant hand gloves and goggles at all times.
• Metals are known to react with sulfuric acid and cause a dangerous explosion. Therefore make sure not to use a metal thermometer when measuring the temperature of the electrolyte.

Method

• First of all, remove the caps from the upper portion of your car battery.
• Immerse the tip of the hydrometer into the car battery’s first cell and squeeze the hydrometer bulb.
• Now release the hydrometer bulb and let the electrolyte enter the hydrometer needle.
• Read the electrolyte specific gravity as per the written instructions on the label of your tool.

Following are the possible readings and their meanings:

• 1.265-1.299: a fully charged battery
• Below 1.265: an undercharged battery

It is best to use a hydrometer that comes with a conversion table so that you can adjust your readings according to the climate.

Conclusion

Knowing the voltage of your car battery is essential to understand the condition it is in. I recommend checking your car battery several times a year and noting down the voltage readings so that you can compare them over time!

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