AGM vs Lead Acid Batteries: 12 Differences 9 FAQs. Agm car battery voltage

The Complete Guide to AGM Batteries

You’ve heard the term AGM battery before and may even know that it stands for Absorbent Glass Mat. But, what does Absorbent Glass Mat (AGM) actually mean and how does that enhance the battery’s performance over standard lead acid batteries?

Let’s review some basics of the SLA (sealed lead acid) battery construction. All SLA batteries are comprised of lead plates (positive and negative) and electrolyte that are then arranged into “cells” and placed into a battery case. Some of these batteries are also valve-regulated, which allows for the escape of minor amounts of gas that occurs during the recombination process during charging. Although these batteries allow gases to escape, they are spill-proof batteries (sometimes called valve regulated lead acid or VRLA), and allow for safe operation in almost any position (the only limitation is they are not recommended to be used upside down). Because they are sealed, you don’t need to add electrolyte after the manufacturing process, and any gases that are generated go into a recombination cycle.


In AGM type batteries, the construction follows the same basics as standard SLA, with the addition of a fiberglass mat that is placed between each negative and positive plate to absorb the electrolyte. Since the mat acts like a sponge with the electrolyte, the battery becomes non-spillable.

The AGM battery holds the electrolyte in place and works by allowing the electrolyte to be passed through the fiberglass mat, creating maximum surface area for the electrolyte to touch the plates without it flooding the battery with too much fluid. AGM batteries contain only enough electrolyte to keep the mat wet and if the battery is broken no free liquid is available to leak out. This allows for less electrolyte in the battery while still providing the same energy as traditional SLA batteries.


When most people think of AGM batteries, they likely think of deep cycle battery applications. However, not all AGM batteries are deep cycle. While a popular choice for deep cycling, as an AGM battery has a depth of discharge (DoD) of 80% versus a standard flooded battery which has a DoD of 50%, it is also a popular choice for starter batteries. This is because it has low internal resistance and can provide high current loads quickly. AGM batteries are also being used as start-stop batteries in modern cars, this is due to flooded batteries not being robust enough to handle the repeated cycling in start-stop applications which can cause the battery to fail after only a couple of years use.

For example, at Power Sonic we offer our AGM technology in both deep cycle AGM batteries (the PDC line) and as a popular option in our PowerSport family (Super Sport, Ultra Sport AGM, and our Stop-Start AGM lines). However, AGM is also the technology we use in our general purpose (PS) and long life (PG) families of products as the Absorbent Glass Mat separator maximizes the surface area of the electrolyte improving battery performance.

Each cell in an AGM battery has 2 volts so AGM batteries are available in a variety of voltages including popular 6V and 12V models.


One of the advantages of an AGM battery is they can be charged up to five times faster than a standard flooded battery. As with all sealed lead acid batteries, AGM are sensitive to over-charging, we recommend this guide to charging sealed lead acid batteries to ensure get the most out of your AGM battery.


Yes AGM batteries are recyclable. than 98% of an AGM battery can be recycled. We in the battery industry are very proud of the fact that lead acid batteries are one of the most highly recycled products on the planet. AGM batteries are environmentally friendly and easy to recycle, they can be recycled at almost all recycling centers, along with many automotive outlets and thousands of other locations.


There are many benefits of AGM technology over its older flooded battery construction. One big benefit of the fiberglass mat is that since the mat holds the acid, the battery is less likely to sulfate. This characteristic is what allows it to reach a deeper DoD than it’s flooded equivalent.

The lower internal resistance of the AGM battery also has a lower self-discharge rate and therefore doesn’t require a topping charge as frequently as a flooded battery would in long term storage conditions. It is important to note that AGM batteries still must be charged before storing and will require maintenance charging while in long term storage but will charge faster than a flooded battery.

Some advantages that AGM has over flooded batteries (as well as faster charging) are increased cycle life and vibration resistance. This is because the combination of the tightly packed AGM battery and the mat inside act as a damper, which are characteristics that lend nicely to power sport applications. Another benefit of the mat is that the battery requires less electrolyte than flooded batteries, which decreases its weight.

However, one of the down sides to the AGM battery is its cost – at slightly higher than flooded, you will pay more for a battery that doesn’t need to be maintained in the same way a flooded battery does. In fact, cost is one of the reasons flooded batteries are still commonplace (usually seen more in motorsport applications).


Another popular alternative to flooded and AGM type batteries is the Gel battery. A Gel battery is still maintenance-free, its cells are sealed, and it uses a recombination process to prevent the escape of its gasses. What varies with a Gel battery is the electrolyte itself is a thixotropic gelled sulfuric acid.

When comparing a Gel battery to an AGM battery, you will see that the Gel battery’s rated capacity will decline much faster than an AGM battery’s as the ambient temperature get colder (below 32 degrees F). A Gel battery is also does not perform as well in high rate or starter applications as an AGM, which is why you don’t see Gel power sport batteries. On the plus side for Gel, it is more acid limited, giving it a slightly longer service life in some applications. Power Sonic offers Gel batteries in our DCG (Deep Cycle Gel) and our 2-volt OPzV Tubular Gel lines.


There are many differences between AGM and lithium batteries. When it comes to choosing the right battery for your application, you need to understand exactly what you are looking to get out of the battery. Is it a deep cycling application, a high rate discharge application or a float standby application? Does the application already have a built in charger for a specific chemistry? What is your budget? etc.

We at Power Sonic have put together a comprehensive guide to the differences between sealed lead acid batteries and LiFePO4 batteries, this should be able to help you to see whether AGM is the better choice for your application.

To summarize, depending on the application and your budget, you will find the AGM battery to be the more superior battery over flooded battery types due to its lower weight, lower maintenance, and overall enhanced performance. You will also find AGM to be a popular choice over the Gel batteries as they are much more common and usually less expensive. The battle between AGM and lithium batteries will depend on your application and what you are looking to get out of the battery.

If you have any questions about which battery is more suitable for your application, please feel free to call or email us.


Find the right battery for your application today. Many of Power Sonic’s wide range of sealed lead acid batteries utilize the latest in AGM technology.

You may also be interested in…

The Comprehensive Guide to Level 2 EV Charging

This comprehensive guide on Level 2 charging for electric vehicles (EVs) covers everything from Level 2 charging speeds and charger types to…

EV Charging Connector Types: A Complete Guide

Electric vehicles (EVs) continue to grow in popularity worldwide due to their clean energy and efficient performance. However, with the incr…

The Benefits of Offering EV Charging at Hotels

As the world moves towards a more sustainable future, electric vehicles (EVs) are becoming increasingly popular. The growth of EV numbers pr…

The Power Sonic Brand Promise


Manufactured using the latest technology and stringent quality control, our battery products are designed to exceed in performance and reliability.


Our focused approach to exceptional end to end customer experience sets us apart from the competition. From enquiry to delivery and everything in-between we regularly exceed our customers’ expectations.


Delivery on time, every time to customer specifications. We pride ourselves on offering tailored service solutions to meet our customers’ exact specifications.

AGM vs Lead Acid Batteries: 12 Differences 9 FAQs

Looking for a mechanic near you for maintenance or repair? RepairSmith brings the shop to you. Get a free instant quote today.

Your car’s starter battery is probably one of two rechargeable battery types — it’s either a flooded lead acid or an AGM battery.

But how do these two batteries differ?

In this article, we’ll compare the AGM vs lead acid battery and see how they stack against each other. We’ll then expand into some FAQs for additional details on these car batteries.

This Article Contains

  • What’s An AGM Battery?
  • What’s A Flooded Lead Acid Battery?
  • What are Sealed Lead Acid Batteries?
  • Is A Gel Cell Battery An AGM Battery?
  • Is An EFB Battery An AGM Battery?
  • What’s A Deep Cycle Battery?
  • Are There Lithium Car Starter Batteries?
  • Can I Use AGM Or Lead Acid Batteries As A Battery Bank?
  • What’s A Reliable Fix For My AGM Or Lead Acid Battery?

AGM vs Lead Acid Batteries: 12 Key Differences

Before we begin the comparison, it’s important to note that the AGM battery has its roots in the traditional lead acid battery. As a result, they do share a few similarities.

Now, let’s see how each battery type contrasts, beginning with its inner workings.

How AGM vs Lead Acid Batteries Work

The AGM battery and the standard lead acid battery are technically the same when it comes to their base chemistry. They both use lead plates and an electrolyte mix of sulfuric acid and water and have a chemical reaction that produces hydrogen and oxygen as a byproduct.

However, this is when they start to diverge.

A. Flooded Lead Acid Battery

The flooded lead acid battery (FLA battery) uses lead plates submerged in liquid electrolyte. The gases produced during its chemical reaction are vented into the atmosphere, causing some water loss. Because of this, the electrolyte levels need regular replenishment.

B. AGM Battery

The AGM battery uses fiberglass mats sandwiched between lead plates. It’s where the battery gets its name – Absorbent Glass Mat (AGM). The glass mat wicks the electrolyte solution, keeping it suspended in place, so it’s not free-flowing.

Because the AGM is a sealed battery, there’s minimal to no off-gassing.

Gases produced during the chemical reaction recombined with the electrolyte.

And if there is excess gas (such as when the battery is overcharged), a vent releases it to maintain internal pressure.

Maintenance Needs

The AGM battery is maintenance-free and can be placed in more enclosed areas as there’s no off-gassing except for the occasional venting. It’s suited for use in vehicles with batteries in trunks and under seats or in locations where maintenance can be hard to do.

On the other hand, the flooded battery requires regular electrolyte servicing and needs to be in a well-ventilated area as it releases gases and steam.

Durability, Vibration And Shock Resistance

The AGM battery tends to be built harder than the flooded lead acid battery, as it originally served military and aviation use.

The sandwiched configuration of glass mat and battery plates in the AGM battery translates to components that don’t fall apart easily. This structure results in a battery that’s shock and vibration resistant — making them favorites in race cars and motorcycles.

Forceful movements and heavy vibrations can damage flooded battery plates, and they need to be mounted securely to minimize these effects.

Mounting Flexibility And Spillage

The glass mat technology in the AGM battery makes it spill-proof and position insensitive. You can mount it in many configurations (just don’t turn it upside down).

However, the flooded cell battery has a liquid electrolyte, so it must always be upright to prevent spills. Spilled electrolyte can cause corrosion if not cleaned up.

Internal Resistance and Power Output

The AGM battery’s internal resistance is among the lowest of the various lead acid batteries. While a new flooded lead acid battery can have an internal resistance of 10-15%, a new AGM battery can be as low as 2%.

Low internal resistance translates to increased battery voltage output.

It also means a reduced loss of heat as power circulates in the system.

AGM batteries also respond to loading better than flooded lead acid or gel batteries. They handle large power demands so well that they’re the go-to lead acid variety for start-stop vehicles.

Charging Time

Low internal resistance also grants the AGM battery faster charging times. Not as fast as a lithium battery, but up to 5x more than a flooded lead acid battery, when using the same power source.

Depth Of Discharge

AGM batteries have an 80% depth of discharge (DoD), which is better than the 50% DoD offered by a flooded cell battery. This makes the AGM battery well-suited to deep cycle applications.

Even so, it’s not recommended to discharge either battery type below 50% of its capacity — unlike the lithium battery, which can be fully discharged.

Note: Depth of Discharge indicates how much battery capacity can be discharged safely without damaging it.

Temperature Tolerance

The AGM battery generally performs better in all temperatures and tends towards good Cold Cranking Amp (CCA) ratings.

The electrolyte that’s held in the glass mat doesn’t expand like a liquid while frozen. This makes AGM batteries resistant to cold weather damage. So while the battery likely won’t work in a frozen environment — it won’t crack, at least.

Flooded lead acid batteries, on the other hand, will freeze in the cold. The battery plates can crack, and the cases can expand and leak.

In extreme heat, the flooded lead acid battery will evaporate more electrolyte, risking the battery plates to atmospheric exposure (the lead plates need to stay submerged).

Sensitivity To Overcharging

Flooded lead acid batteries are much more tolerant to overcharging than AGM batteries.

The sealed aspect of AGM batteries makes them more prone to thermal runaway, which can be triggered by overcharging. Even if you discount thermal runaway, overcharging will shorten an AGM battery’s lifespan faster.

So, when charging an AGM battery, use a regulated battery charger to control the voltage and current going into the battery.

Note: Thermal runaway is when a battery generates too much heat than it can dissipate. The battery will dry out and melt, release toxic chemicals, and cause fires or explode in extreme cases. Nearby batteries will be affected and may result in a domino effect.

Lifespan And Self-Discharge

AGM batteries generally last longer than standard lead acid batteries. Because of their low self-discharge rate, AGM batteries also last longer than their flooded counterparts when not in use.

A well-maintained AGM can last up to 7 years, while flooded batteries typically last around 3-5 years. You’ll know your battery has issues if your car has trouble starting.

Corrosion And Sulfation

The flooded battery is more prone to corrosion than the AGM battery because it can vent acidic steam and is likelier to spill and leak electrolyte liquids.

However, both batteries will suffer sulfation if left in a state of discharge for too long. AGM batteries are a little more resistant, though, partially because they have a slower self-discharge rate.

If you see extensive corrosion on your battery terminals, it’s probably time to contact your mechanic for a replacement battery.


The flooded battery is cost-effective and reliable as a starter battery for standard cars. AGM batteries can be up to 2-3 times more expensive than a conventional battery.

Now that we’ve seen how the AGM battery and flooded lead acid battery compare, let’s go through some FAQs.

Battery FAQs

Here are answers to some frequently asked questions on car batteries:

What’s An AGM Battery?

The Absorbent Glass Mat (AGM) battery was developed in the early 80s as an alternative to NiCd batteries. It’s a type of sealed lead acid battery (SLA battery) that’s maintenance-free and spill-proof.

It’s used in all types of applications — from marine to off-grid power systems and in advanced vehicles with significant power demands.

What’s A Flooded Lead Acid Battery?

The flooded lead acid battery (FLA battery) is the most common lead acid battery type and has been in use over a wide variety of applications for over 150 years.

It’s often referred to as a standard or conventional lead acid battery. You’ll also hear these conventional batteries called a wet cell battery — because of their liquid electrolyte.

If you drive a regular car, chances are, you have a wet cell battery under your hood.

What are Sealed Lead Acid Batteries?

The sealed lead acid battery (SLA battery) is a subset of lead acid batteries. It’s also known as a Valve Regulated Lead Acid battery (VRLA battery).

Unlike wet cell batteries, the sealed battery offers no access to its internal compartment. Instead, it uses a one-way valve to regulate pressure resulting from internal chemical reactions.

Is A Gel Cell Battery An AGM Battery?

The AGM battery is often confused with the gel battery since both are sealed battery types.

However, where the AGM battery uses a glass mat to hold its electrolyte, the gel battery uses a silica agent to suspend its electrolyte in gel form.

The gel cell battery is rarely used in cars as they don’t do well as a starter battery. It’s also very sensitive to overcharging, and the gel can be damaged if this happens.

Is An EFB Battery An AGM Battery?

EFB is short for Enhanced Flooded Lead Acid Battery.

The EFB battery is a flooded battery designed as an improvement over conventional batteries that’s also cheaper than an AGM battery. It’s used in basic start-stop vehicles.

What’s A Deep Cycle Battery?

The starting battery delivers quick bursts of power to start a car engine.

The deep cycle battery is designed to deliver steady power over an extended period of time.

You’ll find the deep cycle battery in backup technology, as alternative energy storage, or in marine vehicles. In fact, it’s also known as a marine battery because that’s one of its most common uses.

All types of lead acid batteries — whether they are AGM, gel cell, or flooded — are used in deep cycle applications. All lithium batteries are “deep cycle,” too.

Are There Lithium Car Starter Batteries?

The lithium ion battery is typically used to power electric vehicles (EVs). It works differently than the conventional lead acid battery, and can’t be adequately recharged by the alternator fitted with a regular car engine.

However, there are lithium starter batteries — used for their lighter weight and compact size in motorsports. The lithium ion battery can also deliver constant power over any rate of discharge.

Will we see lithium starter batteries for regular cars anytime soon?

Probably not, as they’re pretty expensive.

Can I Use AGM Or Lead Acid Batteries As A Battery Bank?

Both the AGM and flooded lead acid deep cycle batteries can act as a battery bank and charge up with a solar panel.

A flooded lead acid battery bank will be a cost-effective setup.

However, it’ll require regular maintenance and may take up more space because the batteries will need to sit upright.

An AGM battery bank would be easier to configure because they can lie on their sides.

They’re also maintenance-free. However, they’ll cost more than a flooded battery bank.

What’s A Reliable Fix For My AGM Or Lead Acid Battery?

Battery problems can crop up at any time, but don’t worry.

It’s easily resolvable with a mobile mechanic like RepairSmith.

They’re a convenient mobile vehicle maintenance and repair solution.

  • Battery repairs and replacements can be done right in your driveway
  • Expert, ASE-certified technicians execute vehicle inspection and servicing
  • Online booking is convenient and easy
  • Competitive, upfront pricing
  • All maintenance and repairs are completed with high-quality equipment and replacement parts
  • RepairSmith offers a 12-month | 12,000-mile warranty for all repairs

For a quick and accurate cost estimate of your battery repairs, fill this online form.

Closing Thoughts

When comparing the AGM vs lead acid battery, you’ll notice that they have a ton of differences. However, there’s one little thing to keep in mind:

If your original battery is an AGM battery, you can’t change it to an FLA battery.

The flooded battery simply won’t have enough juice to meet all your car’s power demands.

As for other battery concerns, you can always rely on RepairSmith for help. Just contact them, and their ASE-certified mechanics will be at your doorstep in a blink of an eye!

RepairSmith RepairSmith is the easiest way to repair your car. Our ASE-certified technicians deliver quality car repair and maintenance directly to your driveway. We offer upfront pricing, online booking, and a 12-month, 12,000-mile warranty.

How To Test AGM Batteries

Absorbent Glassmatt Batteries otherwise known as AGM batteries are modern versions of flooded lead-acid batteries. These batteries are generally used in vehicle batteries.

Many times the batteries lose their voltage and charge due to some abnormal reasons. In order to troubleshoot the AGM battery problem, different battery tests need s to be performed.

There are several tests available to check the AGM batteries based upon the problems caused. In order to troubleshoot the specific problem, you must know how to test AGM batteries.

Incorrect diagnosis of the battery may result in wrong troubleshooting. This may lead to permanent damage to the battery which is not cost-effective.

Testing the AGM Batteries- Step by Step

Let’s Test The Initial Voltage First

Any sort of assembling by unauthorized personnel may lead to voiding the warranty of the battery. Therefore, if you have enough warranty remaining then you can go to the customer service center to get your battery checked and diagnosed.

Considering, the battery has crossed the warranty limit and showing some problems. Then you can perform the initial test to check out the battery health in order to save some buck. You can determine the state of charge of the battery by analyzing the voltage availability of the battery.

Voltage Test Performance

Before performing the actions you must wear silicone-based gloves and goggles for safety and precaution. Be sure to perform the initial voltage after completion of charging the battery.

  • First of all, disconnect and switch off the connections from the battery.
  • Clean up the terminals properly with a clean piece of clothing. Corrosive terminals may not show the real result of the voltages.
  • You can get a voltmeter or a multimeter for proceeding with the test.
  • Connect the cables from the measuring device to the battery and et the reading from the display or the analog dial.
  • Perform the test three times to get an average idea of the voltage ad to avoid errors.

Interpretation of the Results

Depending on the usage and health of the battery, it will show different voltage values which point to the state of charge of the battery.

If your battery shows a voltage rating from 12.7V to 13V then the battery health is very good. Showing voltage below 12V means the battery requires recharging as soon as possible. For such circumstances recharge the battery using a standard battery charger and retest.

If the voltage still falls soon then the battery may have become dead. Again, if your battery shows voltage from 10.5 to 11V. Then it is possible the battery has been discharged due to lack of use and charging. Properly charging using the quick charger can revive the battery if the plate and electrolyte of the battery retain power.

The voltmeter showing reading below 10V means the battery has been completely out of service and requires replacement. No servicing or troubleshooting can revive this battery.

What about the load test?

Performing a load test on your battery test is a way to determine the actual capacity of the battery to perform. Besides, it helps to determine the health of the battery as well.

There are various load testers available in the marketplace. It works on the principle of pressurizing the battery by suckling maximum power out of the battery for a certain amount of time.

Check for the Cold-cranking Amp(CCA) rating of the battery

If the AGM battery is for the vehicle then there will be a label saying the CCA value of the battery. Cold Cranking Amp(CCA) of the battery means the amount of power the battery can put at freezing temperature for 30 seconds.

This process is done by maintaining the voltage at 7V. For average vehicles, the CCA is between 300-700. Vehicles with powerful engines have a higher CCA value

Doing Calculation

You have to divide the CCA of the battery in half. Now, it is done to measure the health of the battery. Considering your battery shows a reading equivalent to half of the CCA after the load test. Then the battery is supposed to be in good health.

On the other hand, if there is a very huge difference seen between the reading of the tester and CCA. then it should be considered that the battery health is not doing good.

Load Test Performance

For the AGM battery load testing, you will require a compatible standard load tester.

  • First of all, make sure your battery is charged to the fullest.
  • Connect the load tester to the battery using the cables. Make sure the terminals are connected in the correct way.
  • Select the testing profile for your AGM battery.
  • Switch on and run the test for 15-20 seconds.
  • Normally the test itself gets terminated after 10-15 seconds.
  • Finally, note down the reading from the testing device.

The result from the test

If you get a value lesser than 10 percent then recharge the battery to the fullest using a quick battery charger. Run the test again for confirmation. If you still get a high-value difference then the calculated value then the battery health is highly depleted. It means the electrode plates have been worn out completely.

Test The Type of Batteries You have

There are different types of batteries available in the market. All have a similar electrochemical reaction productivity principle. But, the difference is in the types of electrolytes, electrodes, construction, etc.

Generally, we see two types of deep cycle batteries. These are the Flooded Lead-acid battery and the Absorbed Glassmatt Batteries. All these batteries get worn out after a certain period of time. Their capability gets reduced and cannot perform well.

For these reasons, it is important to keep an eye on battery health at a regular interval time. Running different diagnostic tests on the batteries you have will help you to keep records.

If some problems are previously detected within the battery then you can also perform troubleshooting beforehand. This will add some additional life to the battery.

If you have a battery and want to run some tests then some series of actions need to be performed. These are stated below.

Inspect the type of battery you have

It is important to know the type of battery you have. This procedure is quite simple. If you are pouring distilled water to the cell chambers of your battery then it is a conventional lead-acid battery. Apart from that, it is most probably the Absorbent Glass Matt battery.

Another way to differentiate the type of battery is the electrolyte type. Flooded batteries use liquid acid electrolytes. And so the weight of the battery is higher. On the contrary, AGM batteries gel-based electrolytes. These batteries are comparatively lighter than others.

Inspection and determining the State of Charge of the battery(SoC)

This process is simple and only requires a digital multimeter or voltmeter. After fully charging your battery you have to connect the battery to the volt measuring device. Fully charged batteries show a voltage reading of more than 13V.

discharged batteries show a lesser amount of voltage reading in the voltmeter or the multimeter. Following the given chart you can determine the SoC of the battery.

Voltage Reading Charge Percentage Interpretation
13V 100% Good health
12.5-12.8V 90% Good Health
12.2-12.5V 70% Moderate Health
11-12V 60% Heavily Discharged
Below 11V 40% or less Flat battery

Heavy load Testing of the battery

Load testing is the same in all the batteries. It is better to keep your battery charged up to 80% or more for a more reliable result. For load testing, you can use the automatic Smart chargers.

This charger can charge all sorts of batteries with a specific charging profile. over, there are some quick chargers that can also be used. Always make sure the charging environment should be very well ventilated.

The portable Conductance Testing

  • Firstly, clean up the terminals of the battery. Corrosion in the battery terminals reveals false reports.
  • Connect the tester to the battery appropriately.
  • Run the test. It takes only 15-20 seconds to complete the test.
  • These portable testers give very straightforward replies.
  • You will get a positive or negative remark based on the health of the battery.
  • It is helpful to determine whether or not you should get a replacement for the battery.

Half-CCA Load testing

  • First of all, note down the CCA of the battery and divide the value by 2.
  • Connect a full-fledged load tester to the battery.
  • Select the specific testing profile and run the test.
  • Getting a somewhat equal value to the half of the CCA means good battery health.
  • A difference of more than 10% of the calculated and reported value means the battery is dead.

All the testings should be done with a good state of charge of the battery. over, the testings should be done at least three times to avoid technical and marginal errors.

Do you want to know the battery charge?

AGM or lead-acid batteries do not come with a digital display that shows the amount of charge it has. In order to know the exact amount of charge your battery is retaining can be known by some actions. For this, you have to have a digital voltmeter, wattmeter, or multimeter.

Initial Inspections

First of all, make sure your battery is not connected to any of the electronic appliances. Connected appliances may give false data.

Take readings

  • Firstly, connect your multimeter or voltmeter to the battery using the cables.
  • The connection should be appropriate.
  • Set the scale on the multimeter and run the device.
  • Note down the voltage reading.
  • Now comparing the voltage of the battery you can convert it to the state of charge according to the given data.

Does your battery have cranking power and capacity?

The cranking power of the battery is the capacity of the battery to output amperage constantly for a certain period of time. It is an important aspect for vehicles. Good-rated Cranking power instantly boots up the vehicle. Batteries with lower cranking power cannot start the vehicle engine.

lead, acid, batteries, differences

In order to know the cranking power, you can perform the load test on your battery. During the load test, the measuring device sucks a massive amount of power from the battery for 10-15 seconds.

You can run a manual test to determine the latest cranking power of the battery. For this, you will require a voltmeter and a battery tester that has a built-in mode.

  • At first, connect the voltmeter to the battery using the proper connection to the terminals.
  • Note down the data. Most of the good batteries will show a voltage reading above 12.6V. Normally, the battery is said to be 12V. But it depends upon the state of charge.
  • Then connect the battery tester to the battery and select the cranking amp mode.
  • You have to input the CCA rating of your battery to the device.
  • Run the test. The battery tester device will automatically do calculations based on the data and will show you SoC, Health, etc.

Finally, do an overall battery test

The best way to determine the health of the battery is to perform a heavy load test. The battery load tester pulls out some massive power in amps. If the voltage of the battery is maintained properly then the health of the battery is considered to be good.

For this, the Cold Cranking Amp rating of the target battery should be noted down. You may require an extra voltmeter if the battery tester doe not have one.

  • Connect the battery tester to the battery. It is done by connecting the positive terminal of the battery to the positive terminal of the tester. And the negative terminal of the tester to the negative terminal of the tester.
  • Check out the volt reading in the tester or the voltmeter. When fully charged the reading should be around 12.5-12.6V
  • Run the test by inputting the cranking amp amount manually or digitally to the tester. It should be done within 15 seconds.
  • Three consecutive tests should be performed with 5-10 seconds of interval or break.

If the battery health is good, the voltage during the test never drops down to 10V. But the battery is depleted the voltage omes below to 10V. This means the battery requires replacing or maintenance.

How to tell if your battery is dead or not?

Over regular usage, the health of the battery runs down on a regular basis. That is why regular maintenance and diagnosis of the battery are required. Otherwise, on some fine day, the battery will be dead suddenly without prior notice.

  • Check the voltage readings of the battery on regular basis.
  • Inspect the battery voltage at 100% SoC. If the battery voltage runs below 12.6 at a very short time. Then it means the capacity to hold a charge is degraded.
  • over, instant load or stress tests should be performed.
  • If at any point during the test, the voltage reading goes under 10V then the battery is considered to be dead.

Tips to improve the battery life of AGM batteries

In order to, improve the health of the Absorbent Glass Matt some actions can be taken. Even though the AGM batteries are maintenance-free, regular inspection and diagnosis can help get battery life.

  • You can use anti-corrosive cables for making battery connections.
  • Clean the battery terminals on a regular basis. Corrosive terminals show poor performance in the delivery of the power.
  • Check the voltage reading of the battery on a regular basis.
  • Use a standard automatic Smart battery charger to charge the battery slowly to the fullest occasionally.
  • Inspect for the physical damage to the battery.
  • If you are using the flooded battery, then pour the acid water on a regular basis.
  • Operate the battery at optimum temperature. Very hot or cold temperatures may degrade the battery’s health quickly.
  • Do not over-stress the battery than the limit.

If you still have any confusion, follow the tutorial video below about – how to test an AGM battery.

Frequently Asked Questions about Testing AGM Battery

In this section, we shall learn about the general questions about battery testing in the mind of the consumers.

Do AGM batteries go bad?

AGM batteries have a limited working life like all other batteries. But compared to other batteries, the longevity of the AGM battery is very high. It can effectively operate up to 5-7 years at a stretch.

How do you rejuvenate an AGM deep cycle battery?

Restoring deep cycle AGM batteries is tough but not impossible. For kick-starting, you can connect the target battery with a good AGM battery in parallel. Then using a heavy quick charger the good battery should be charged for about 1-2 hours. After getting a decent voltage reading the original battery should be connected to a Smart slow battery charger for restoring.

When should the AGM battery be replaced?

If considering your AGM batteries fail to retain power, hold the charge and drop in voltage rapidly. Then you should think of replacing the battery with a new one. A load test will also help you know the battery status.


Absorbent Glass Matt or AGM batteries are a part of people’s life. The vehicles nowadays mostly relies on the AGM battery. over, these batteries don’t come cheap. That is why it is quite important to keep track of the battery’s health and battery status.

For doing this, you must know the correct ways to test the AGM batteries. Because incorrect diagnosis will lead you to take bad decisions which won’t be fruitful in the future. There are several automatic and manual ways to test the AGM batteries. This article would help you to select teh best possible way to test the AGM battery.

Hi, Marcelo Araujo-Xavier is here! I am the author of Batteryhint. I have been working in the battery industry for over 20 years and have a passion for helping people find the best battery for their needs. I have personally tested and reviewed hundreds of different batteries. I’m certified by the International Association of Automotive Battery Manufacturers. I have always been interested in batteries and how they work, so I decided to start this website to share my knowledge with others. I hope you find the information on this website helpful and informative. I will be regularly updating this website with new resources, If you have any questions or Комментарии и мнения владельцев, please feel free to contact me. I would love to hear from you and help you find the best battery for your needs.

Lead Acid Battery Voltage Charts (6V, 12V 24V)

Just so you know, this page contains affiliate links. If you make a purchase after clicking on one, at no extra cost to you I may earn a small commission.

Here are lead acid battery voltage charts showing state of charge based on voltage for 6V, 12V and 24V batteries — as well as 2V lead acid cells.

Lead acid battery voltage curves vary greatly based on variables like temperature, discharge rate and battery type (e.g. sealed, flooded). The voltage to battery capacity chart in your battery manual should always take precedence over the generic, averaged ones listed below.

Note: Estimating state of charge based on open circuit voltage is only accurate when batteries are at room temperature and have been resting — i.e. disconnected from all loads and chargers — for several hours.

V Lead Acid Battery Voltage Charts

Printable Chart


6V lead acid batteries are used in some DC devices like lights, pumps and electric bikes. You can also wire two in series to create a 12V battery bank. They are made by connecting three 2V lead acid cells in series.

lead, acid, batteries, differences

6V sealed lead acid batteries are fully charged at around 6.44 volts and fully discharged at around 6.11 volts (assuming 50% max depth of discharge).

6V flooded lead acid batteries are fully charged at around 6.32 volts and fully discharged at around 6.03 volts (assuming 50% max depth of discharge).

V Lead Acid Battery Voltage Charts

Printable Chart


12V lead acid batteries are popular in solar power systems and other 12V electrical systems. They’re widely available and have a low upfront cost. Many car and marine batteries are 12V lead acid batteries. They are made by connecting six 2V lead acid cells in series.

As far as I can tell, lead acid is still the most popular rechargeable battery type for DIY solar power systems. Lithium iron phosphate (LiFePO4) batteries have become a lot more popular in recent years, though, in large part thanks to their dramatic price drops we’ve seen over the last decade.

12V sealed lead acid batteries are fully charged at around 12.89 volts and fully discharged at around 12.23 volts (assuming 50% max depth of discharge).

12V flooded lead acid batteries are fully charged at around 12.64 volts and fully discharged at around 12.07 volts (assuming 50% max depth of discharge).

V Lead Acid Battery Voltage Charts

Printable Chart


24V lead acid batteries are another common option for solar power systems. Working with higher voltages helps keep amperage low, saving you money on wiring and equipment. They are made by wiring in series twelve 2V lead acid cells or two 12V lead acid batteries.

24V sealed lead acid batteries are fully charged at around 25.77 volts and fully discharged at around 24.45 volts (assuming 50% max depth of discharge).

24V flooded lead acid batteries are fully charged at around 25.29 volts and fully discharged at around 24.14 volts (assuming 50% max depth of discharge).

V Lead Acid Cell Voltage Charts

Printable Chart


Individual lead acid cells have a nominal voltage of 2 volts (sometimes listed as 2.1 volts). You can buy 2V lead acid cells and connect them in series-parallel configurations to build a battery bank with your desired voltage and capacity.

2V sealed lead acid cells are fully charged at around 2.15 volts and fully discharged at around 2.04 volts (assuming 50% max depth of discharge).

2V flooded lead acid cells are fully charged at around 2.11 volts and fully discharged at around 2.01 volts (assuming 50% max depth of discharge).

Ways to Check Lead Acid Battery Capacity

Measure Open Circuit Voltage with a Multimeter

Pros: Accurate

Cons: Must disconnect all loads and chargers and let battery rest for several hours

To properly estimate battery capacity based on open circuit voltage, first disconnect everything from your battery and let it rest at room temperature for several hours. (Battery University recommends at least 4 hours.)

Then, simply use a multimeter to measure the voltage at the battery terminals and compare the number you get to the state of charge chart in your battery manual. If your battery manual doesn’t have a chart, use the relevant one listed above.

For example, I recently wanted to test the remaining capacity of a 12V 33Ah sealed lead acid battery I own. The battery was already at rest and at room temperature — it had been sitting disconnected in my basement for the past couple weeks.

So I grabbed my multimeter, prepped it to measure DC voltage, and touched the probes to the battery terminals. I got an open circuit voltage of 12.63 volts.

I couldn’t find my battery’s manual, so I referred to the 12V sealed lead acid voltage chart above to estimate its capacity. Based on that chart, I’d estimate it had about 80% capacity left.

Check Specific Gravity with a Hydrometer or Refractometer

Pros: Accurate

Cons: Only works for flooded lead acid batteries

You can use a hydrometer or refractometer to measure what’s called the specific gravity of your lead acid battery. Measuring the specific gravity is another way to estimate state of charge.

Because this method requires you to open the battery to access the electrolyte solution inside, it only works with flooded batteries.

I’ve only ever used sealed lead acid batteries, so I unfortunately can’t run you through the steps on how to do this. Refer to the steps listed in your battery manual, or the product manual for your hydrometer or refractometer.

lead, acid, batteries, differences

Use a Solar Charge Controller

Pros: Convenient

Cons: Inaccurate

If you’re using your lead acid battery in a solar power system, your charge controller probably measures battery voltage for you.

You may be thinking you can just use this reading to get an accurate estimate of your battery capacity. Unfortunately, using battery voltage to estimate capacity while the battery is connected to chargers and loads is very inaccurate.

Battery voltage varies greatly depending on factors like temperature and rate of discharge. Plus, the battery voltage reading given by some charge controllers can be inexact. Some charge controllers only display one decimal place, and others have wide margins of error. For example, one cheap PWM charge controller I tested claimed a battery voltage margin of error of ± 0.2 volts.

Still, I know most DIY solar enthusiasts will use this reading most often, if not exclusively. It’s a hassle to disconnect everything from your battery and let it rest just to measure its state of charge more accurately.

If that’s you, just keep in mind how inaccurate this number can be. Don’t think you can know the precise state of charge of your battery from it. Just use it to get a general idea of whether or not your battery is close to being fully charged or discharged.

Lead Acid Voltage FAQ

Note: To reiterate, the recommended voltages and state of charge chart in your battery’s manual should take precedence over the generic ones listed below.

What is the voltage of a fully charged 12V lead acid battery?

A 12V sealed lead acid battery will have an open circuit voltage of around 12.9 volts when fully charged.

A 12V flooded lead acid battery will have an open circuit voltage of around 12.6 volts when fully charged.

To accurately estimate a battery’s capacity based on its voltage, you must first disconnect all loads and chargers from the battery and let it rest at room temperature for several hours.

What is the minimum voltage of a 12V lead acid battery?

The minimum open circuit voltage of a 12V sealed lead acid battery is around 12.2 volts, assuming 50% max depth of discharge.

The minimum open circuit voltage of a 12V flooded lead acid battery is around 12.1 volts, assuming 50% max depth of discharge.

How much can you discharge a lead acid battery?

Many lead acid batteries can only be discharged up to 50%. Discharging them more can cause permanent damage. You should never completely discharge a lead acid battery to 100% depth of discharge. Doing so can shorten its lifespan greatly.

Here is a graph showing the relationship between depth of discharge and life cycles for non-deep-cycle lead acid batteries:

As you can see, consistently discharging a lead acid battery to 100% can severely shorten its lifespan.

What is the float voltage of a 12V lead acid battery?

The float voltage of a sealed 12V lead acid battery is usually 13.6 volts ± 0.2 volts.

The float voltage of a flooded 12V lead acid battery is usually 13.5 volts.

As always, defer to the recommended float voltage listed in your battery’s manual. Some brands refer to float as “standby.” Sometimes, the float voltage will even be listed on your battery label.

How I Got the Numbers in These Charts

To get the numbers in the voltage tables above, I looked up the datasheets for 7 popular brands of lead acid batteries. I found the state of charge charts in each and averaged them together for the final values.

Here are the datasheets I used for the sealed lead acid values (2 AGM, 2 gel), along with the page number where I found the voltage chart:

And here are the ones I used for the flooded values:

Creating these charts was far from an exact science. Only a couple of the datasheets listed open circuit voltages by capacity in table format with exact numbers. Often, they included a graph from which I’d have to infer the numbers. What’s more, the graphs often had wide bands rather than thin lines, as if to convey a margin of error or range of possible values — what I came to see as the brands hedging against providing an exact number.

Other brands provided exact numbers, but only for 0%, 25%, 50%, 75%, and 100% capacity values. From these I had to create linear functions to estimate the values between them.

I calculated all the numbers for 2V lead acid cells first, then multiplied these values by the respective number of cells in series to get the values for 6V, 12V and 24V batteries. Finally, I rounded all the values to two decimal places.

Leave a Comment