AGM battery charger: how to choose the right one

AGM battery charger is standard in a wide range of applications.

You can use them to power your car or electronic devices or as a backup power source for the UPS.

However, to make your AGM batteries live longer, it is essential to charge them correctly and use the right charger.

What is an AGM battery?

AGM battery is a lead acid battery that uses a different technology from traditional batteries.

Here, AGM stands for absorbed glass mat.

Unlike standard lead acid batteries, which have a liquid electrolyte, these batteries have a mixture of acid and water that remains absorbed on the fiberglass mats, thus not free-flowing.

Advantages of AGM batteries:

  • Charging time is less than other lead acid batteries
  • Long-lasting
  • Maintenance-free as no watering is required
  • As the electrolyte is present in solid form, there are no chances of spills and leakages
  • Lower self-discharge rate
  • No acid stratification

Charging AGM batteries with different chargers

As the electrolyte is absorbed on the glass mats and is not in liquid form, the way of charging is also different.

Unless a charger says explicitly that it is suitable for AGM batteries, they may not be safe for AGM batteries.

Can I charge AGM batteries with a standard charger?

The answer is NO. Using a regular flooded battery charger for AGM batteries is unsafe as it may cause them to burn out or die.

Some chargers mention “may be suitable for AGM batteries”; however, even such chargers are not recommended for AGM batteries.

If the charger says, “ deep cycle/Gel/AGM.”

Some old chargers mention “Deep Cycle/AGM/Gel,” which means these chargers can charge Gel, deep cycle batteries, and AGM batteries.

However, Gel and deep cycle chargers may charge AGM batteries but will harm them over time.

If the charger says, “Work with all lead-acid batteries.”

If the charger mentions something like “Work with all batteries” or “Work with most lead-acid batteries,” don’t buy them for AGM batteries.

Although such chargers will not harm an AGM battery correctly, they may lead to slow charging or damage over time.

Not all AGM chargers are worthy of the name.

Some chargers that mention AGM as the suitable battery type may also cause issues with the battery over time because such chargers do not charge the battery fully, but only around 85%. 

As the full charge voltage of most lead-acid batteries falls in the range of 13.6 to 14.4 volts, most chargers are designed accordingly.

However, the full charge voltage of the AGM batteries is around 14.6-14.8 volts.

Such chargers will not charge the AGM batteries to their full potential, gradually leading to a “memory effect” ( the battery remembers 85% of the fully charged state).

Also, the battery will die much quicker than the exact specification due to undercharging the battery.

Battery chargers

Battery chargers

AGM battery charging tips

How to maintain the battery when charging?

Charge AGM batteries at the right temperature:

All AGM batteries have a specific temperature range to charge safely.

A temperature above 40 degrees Celsius is unsuitable for most lead acid batteries; cold temperatures below 0 degrees are also unsafe for charging AGM batteries.

So, ensure that the temperature falls within the range of 0-40 degrees Celsius for the long life of the battery.

Fully charge the AGM battery every time:

The full charge voltage refers to the voltage the battery will reach, irrespective of the charging voltage the battery provides.

For a battery’s long life, ensure that it charges to its full charge voltage.

Don’t trickle your AGM battery:

Though no electrolyte flow is inside the battery, permanent charging will eventually dry out the batteries.

When the battery is fully charged once, store it or use it as usual.

Charge the battery once a month; even overnight charging will charge the battery fully.

As AGM batteries have a slow discharge rate, you need not keep them on permanent charging mode as you do with regular lead acid batteries.

Keep your maximum discharge down to 50%. For AGM batteries, it is 12.1 volts.

Discharging an AGM battery lower than 12.1 volts will reduce its life. 

Buy the recommended charger.

Determine the Charger Types:

While looking for a charger for your battery, firstly, you must ensure the type of battery you use.

Several types include VRLA, Gel, AGM, wet cell, etc.

As mentioned earlier,  AGM batteries are very sensitive and need a specific charger for charging.

So, always get a fully optimized AGM battery charger for your AGM batteries.

Determine the battery size:

As said above, battery size means the battery’s voltage, i.e., no. of amperes a battery receives in an hour.

A solar AGM battery has a voltage of 100 amps per hour. If you use a ten amps battery charger, it will take around six hours to fully charge the battery (here, we assume it is 50% discharged).

Alternatively, if you use a 20-amp AGM charger, the time will reduce to half, i.e., 3 hours.

The time a charger takes to charge a battery is calculated as follows:

Amp hours of battery/charger rating in amp/hour.

To this, add 15% additional time for the complete top-off.

If you want quick charging for the battery, you must use a charger with a high amps rating.

However, if you have enough time, use an AGM battery charger with fewer amps.

You must know that charging a battery with a less amps charger will ensure a long and healthy battery life.

Also, it will cost you less money than high amps chargers.

Determine the desired charging performance.

Get a small charger with fewer amps if you want a boat, bike, aircraft, or classic car charged during the off-season.

A small charger will charge the battery slower, but that should not be a problem in the off-season as you won’t be using the vehicle anyway.

On the other hand, if you need fast charging for vehicles such as wheelchairs, get a charger with higher amps.

Conditioning AGM batteries:

Like all other batteries, AGM batteries also undergo sulfation, the build-up of lead sulfate crystals around the battery plates.

More than 80% of the batteries die due to sulfation.

Though you cannot avoid sulfation in the batteries, you can always reverse it.

De-sulfating chargers can remove the sulfation around the battery plates during charging.

Desulfating the AGM batteries increases the battery life by two to three times.

Apart from the desulfation charger, you can also get a desulfator to enhance the life of your AGM batteries.

Desulfator is a small device that attaches to the battery permanently and gives high-frequency pulses leading to the breakdown of lead sulfate crystals.

As a result, sulfation gets removed as soon as it builds up.

The best AGM battery chargers

Rank 1234
AGM chargerCTEK MXS 10NOCO Genius 10 UKCTEK MXS 5.0NOCO Genius 5 UK
Battery typesAll types of 12V lead acid batteries (gel, wet, flooded, AGM, silver ca/ca)All types of 6V/12V lead acid batteries (gel, EFB, wet, Flooded, AGM, silver ca/ca)All types of 12V lead acid batteries (gel, wet, flooded, AGM, Silver Ca/ca)All types of 6V/12V lead acid batteries (gel, EFB, Wet, flooded, AGM, silver ca/ca)Except for 6 volts AGM battery
Dimensions 20L*10W*20H cm9.14L* 5.84W*18.03H cm27.2L* 14.4W* 5.4H cms7.37L*4.83W*11.68 H cms
Waterproof (to IP65)Yesyesyesyes
Charging rate 10 amperes10 amperes5 amperes5 amperes
The capacity of the battery it will charge20-300 amp hoursUp to 230 amp hours1.2-110 amp hoursUp to 160 amp hours for maintenanceUp to 120-amp hours


So, next time you charge your AGM batteries, remember the above tips and suggestions.

For any help with AGM battery cables, contact Cloom, and you can get help from our professionals.