While you can charge an AGM battery using a regular charger, it is better to charge it with a charger with an AGM setting option to reduce the risk of overcharging or undercharging which is harmful to the battery long term.
An AGM battery charger or multifunction battery charger with the AGM option will usually charge the AGM battery to about 14.8V.
The charger may stop the charge once attained or switch to float mode to keep the battery topped up.
Fortunately, more modern chargers have the AGM battery charger option.
How to charge an AGM battery so that it lasts
There are 3 important considerations to keep in mind when charging an AGM battery so that it lasts for as long as possible.
- Provide for good air circulation and use recommended charge rates to keep the battery temperature 5 °F (-15°C )-122°F (50 °C). Exposing the battery to higher temperatures shortens its life.
- Limit the charging current to manufacturer-recommended levels usually up to 10% of its AH capacity
- Make sure the charger is set to charge up to 14.8V or the charger mode is set to charge AGM batteries (this automatically sets the charger voltages to those suited to AGM batteries. This way, your AGM battery will be fully charged.
Unlike wet Lead-Acid batteries, AGM batteries need to be charged to a higher voltage (14.8) compared to wet batteries (14.5V) for a preset time to prevent partial charging.
How to choose an AGM battery charger (4 key features!)
I am going to share with you 4 key features I look for in an AGM battery charger in addition to confirming good product reviews.
# 1. Check that your charger has the option to charge AGM batteries
Better still, buy a charger that can charge different chemistries (wet, AGM, Lithium) in case you plan to charge to a different battery type in the future.
# 2. Confirm that your battery charger has the temperature compensation feature. With this feature, there is a lower risk of overcharging or undercharging as the charger adjusts the charging current depending on the surrounding temperature.
# 3. Does your charger have reverse polarity protection? This feature prevents damage to the charger should the battery cables be accidentally interchanged.
# 4. Select a battery charger with a suitable charging current for your battery.
A battery charger with a higher charge current charges faster and is suitable for larger batteries 80Ah+.
A 10A charger charges faster than either a 5A or 8A battery charger for example.
# 1. Is a float charger good for an AGM battery?
A float charger helps keep your AGM battery fully charged.
This works great when your battery is going to remain unused for several months for example in a parked car or is being used as an emergency power source.
With a float charger, there is no need not worry about finding your battery discharged because of a parasitic load or self-discharge for example.
Unlike a trickle charger that constantly charges the battery, the float charger only charges the battery when battery voltage drops and will shut off again once it is charged.
Note: Whereas a float charger may be able to fully charge your battery, it is slow.
Therefore you need a primary charger to provide the initial charge and the float charger to maintain the voltage or once single charger with a float charge feature.
# 2. How hot should you allow your AGM battery to get?
It is normal for an AGM battery that is being charged to feel warm.
While AGM batteries typically have a design operating temperature life of 5 °F (-15°C) -122°F (50 °C), their life is shortened when they are consistently exposed to AGM batteries to temperatures close to and above 5 °F (-15°C )-122°F (50 °C).
For example, a battery used in float service mode maintained at 77 °F (25 °C) may last for 5 years or more. However, when it is consistently exposed to 122°F (50 °C), its service may be reduced to as little as 1 year.
You can also monitor the battery temperature using an infrared thermometer.
To keep the battery temperatures close to the normal operating temperature of 77 °F (25 °C), keep the charging current to within 10% of its capacity.
In addition, keep the batteries cool by installing them in a shaded area away from direct sunlight.
Also, mount the batteries in an area with good air circulation or use fans to keep the batteries cool.
What to do when the battery is overheated
Should your battery show signs of overheating, immediately disconnect the battery from the charging source and allow it to cool.
Try to investigate the likely cause of overheating: Was it because of overcharging – charging at extremely high currents? Was the battery charger set to the wrong charging mode other than AGM? A faulty charger?
Try to rectify the likely cause of the overheating.
Once cool, if the battery is not fully charged, charge it fully and conduct a load test.
Hopefully, it can still hold a charge. If not, arrange to replace it.
# 3. What happens when a battery is overheated?
An overheated battery may deform, explode and become permanently damaged.
Therefore aim to keep your battery temperature to 5 °F (-15°C )-122°F (50 °C) or the manufacturer recommended range.
# 3. Why do AGM batteries take so long to charge?
Charging AGM batteries does not take a long time compared to wet lead-acid batteries.
How fast a battery charges depends mainly on the charging current used.
Using a higher charge current can result in overheating and permanent damage to the battery and how deeply discharged it is.
To get an estimate of the time it takes to fully charge an AGM battery, use the calculator below.
While you may be able to charge your AGM battery with a regular charger, to minimize the risk of overcharging or undercharging, use a battery charger with the option to charge AGM batteries.
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