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.

More 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 ReadingCharge PercentageInterpretation
13V+100%Good health
12.5-12.8V90%Good Health
12.2-12.5V70%Moderate Health
11-12V60%Heavily Discharged
Below 11V40% or lessFlat 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. Moreover, 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. Moreover, 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.
Voltage ReadingState of Charge

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.

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.
  • Moreover, 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.

Is your AGM battery dead?

  • A dead AGM battery fails to supply the required amount of power to the appliances. 
  • It cannot retain the state of charge for a long time.
  • A fully charged AGM battery when dead, shows instant dropping of the voltage reading when connected to the voltmeter.
  • Moreover, during the load test at a specific CCA rating, the voltage drops below 10V. This shows the battery is bad.

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. Moreover, 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.

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Marcelo Araujo-Xavier

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 comments, please feel free to contact me. I would love to hear from you and help you find the best battery for your needs.

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