How To Charge AGM Battery- Everything You Need To Know

AGM (Absorbent Glass Mat) battery can’t perform appropriately if it’s not perfectly charged. Using an improper charger, charging with the wrong period, etc. can lead the AGM battery to death. Therefore, you should keep a clear conception of how to charge AGM battery.

Along with maintaining the correct voltage and current flow, you also need to maintain the temperature. AGM batteries get charged in three stages. Without understanding the charging cycles, you can’t ensure its full charging. 

Another important thing is to perform a successful charging connection. You can easily start the charging process after going through these parts. There might be bare issues like overheating and many more. All the solutions can be found here. Here you’ll also get a complete guideline on charging the AGM battery using solar panels. 

Can you use a regular battery charger on an AGM battery?

Using a regular battery charger on an AGM battery is just about following some easy steps. The first step starts with monitoring the current setting. The charging rate shouldn’t exceed the rate of 0.15C. Along with this, the voltage should be monitored strictly. 

You can use a multimeter to measure the charging voltage. There might be an overcharging issue if the absorption voltage is exceeded by 0.2V. You should disconnect the charger from the AGM battery after it crosses 14V for 4 hours. 

However, disconnecting the charger at the perfect time is a mandatory move. Unless you perform it timely, the battery may face severe damage. The optimum time is 20 hours after establishing the initial charging connection. 

The proper way to charge AGM battery faster

For the longevity of AGM batteries, you should know how to charge AGM batteries perfectly. Let’s know about setting the AGM battery charger in the right manner. 

Proper AGM battery charging setting

The first thing about the AGM battery charging setting is the temperature. You should set the temperature around 0-40 degrees Celsius. The charging rate should be 0.1 C or 0.2 C for better results. You can maintain the voltage level between 14.6-14.8 V for general purposes. When dealing with a normal charger, never let the battery be overcharged. 

Here are some easy steps you should follow to charge an AGM battery. 

Step:1- Get a charger

  • Get a smart charger that has dedicated AGM mode. 
  • The charger must cope with three stages of charging. Your charger should perform bulk charging as well as float charging simultaneously. 

Step:2- Set the charger

  • First of all, select a well-ventilated space that comes with room temperature. 
  • Then, set the charger to the approximate battery voltage. You also need to set the charge rate at the same time. 
  • For a 20Ah battery, the calculation of ampere will be 1 unit. You need to get a charge rate of 0.1C at any cost. 

Step:3- Select the desired mode

  • Now, select the AGM mode from the charger. It’s all about finding the desired mode and tapping on it. 

Step:4- Connect the charger

  • The last move is to connect the charger and wait for a few hours. Mind the polarity strictly while connecting the charger. 
  • It’ll take around 18 hours to finish the whole charging process. There might be an indicator to remind you about the charging state.

What amp to use to charge your AGM battery?

The first task is to select the suitable model according to your battery from your charger. It’s suggested to charge an AGM battery at the equivalent in ampere of 0.1C or 10% of its capacity in Ah. To make the calculation easy, you can multiply the battery’s capacity by 10%. If you’re looking for any specific recommendation, then a low ampere (1-10) charger could be your pick. 

What is the right voltage to charge an AGM battery?

Maintaining the right voltage is one of the mandatory moves for charging an AGM battery. The AGM battery requires a little bit more voltage than a lead-acid battery. Within 14.6-14.8V, the AGM battery gets charged most of the time. But, when it’s about open-circuit voltage, the voltage should lie between 11.4 to 12.7V. 

Let’s see the AGM battery charging voltage chart

Here is a chart of open-circuit voltage with AGM battery state of discharge. 

State of chargeOpen-circuit voltage
100%12.7-13.0 V
80%12.5-12.7 V
60%12.3-12.5 V
40%12.0-12.2 V
20%11.8-12.0 V
10%11.7-11.9 V
0%11.4-11.6 V

How long does it take to charge an AGM battery?

The time of charging an AGM battery depends on the degree of discharge. To determine the charging time, measure the average voltage using a voltmeter. The ampere should be calculated too for this purpose. Usually, it takes up to 6 hours to charge an AGM battery properly.

If the ampere is 40A for a 200AH battery, the battery will be 100% within 5 hours. When you get the output voltage of 13 volts, that indicates its full charge. Hence, you can get that result after the depicted time.

Do you want to charge an AGM motorcycle battery?

Charging an AGM motorcycle battery is all about maintaining some easy steps. Here are the pro tips to charge AGM motorcycle batteries.

  • Select the suitable charger first. The “low and slow” charge should be followed for charging AGM motorcycle batteries. 
  • You need to find the appropriate amperage charger for the AGM battery. By dividing its amp/hour rating by the amp charge going into it, you can calculate the charging time. 
  • Observe the voltage rating with a voltmeter from time to time. The reading should be approximately 12.4 volts. You need to perform the quick charge if the required voltage isn’t achieved. 
  • The last move is to wait for a certain time. After the expected period, the battery will be charged. 

What about charging AGM batteries with solar panels? 

You can also charge AGM batteries with solar panels. Here are a few steps to follow to charge AGM batteries with solar panels. 

Step:1- Purchasing a charge controller

You need to check the wattage status first from the rear side of the panel. By dividing the solar watt rating by the voltage of the battery, you can assume the right charge controller. Suppose, the solar panel is 300W and the battery is 12V. Then, you need to divide 300 by 12 and the result will be 25. So, the charge controller of 25 amperes is required in that case. 

In case you’re concerned about better efficiency, you can pick an MPPT charge controller. This charge controller is 30% more effective while you need to store as well as transfer energy. Though going for an MPPT requires extra money, you can benefit a lot. 

Step:2- Setting the controller properly

Firstly, place the charge controller somewhere grounded. The next move is to connect the negative and positive wires with the battery properly. Using the red wire as the hot wire and the black one for the negative is recommended. For ensuring a safe connection, the battery should be connected before the solar panel. 

The end of the negative and positive wires should be inserted in the desired ports now. You need to use the right-sized wire for desired performance. For a 12V battery, you should use a 10 or 16 gauge wire. You can take the help of MC4 connectors to connect the wires. The last task is to tighten the wires using a screwdriver. If the output is perfect on the charge connector, then you’re done with it. 

We added a tutorial video below about – how to charge and test an AGM battery. Follow the video for a better understanding:

Frequently Asked Questions

This part is prepared with some necessary questions related to charging AGM batteries. 

Can I charge an AGM battery with a lead-acid charger?

A lead-acid battery charger isn’t highly recommended to charge an AGM battery. But, in case you don’t have an alternative option, you can charge. The charging process must require continuous monitoring. But, it’s recommended to go for a regular AGM battery charger. 

Can I charge an AGM battery with a lithium charger?

Using a lithium battery charger for charging an AGM battery is completely okay. The optimum voltage of AGM batteries lies between 14.1-14.4V. As the interval is almost close to the lithium battery charger, so you can use it. But, you may face minor charging complexity as well as charging speed issues.

Conclusion

Charging an AGM battery isn’t something like rocket science. Now, you have a clear idea of how to charge AGM battery with some simple steps. AGM batteries are sensitive and require a constant charging process. Any mistaken step can lead an AGM battery even to death. 

The first move should be picking an appropriate charger along with a charging outlet. You need to set the charger to combine with the battery voltage. Once the battery starts to be charged, all you have to do is wait. You can monitor the charging in the meantime with the help of the added chart here. 

There might be a heating issue which can make you stressed. It’s common to produce a certain amount of heat while going through the charging phase. By maintaining all the steps strictly, you can come to the desired end. 

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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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