How to Maintain AGM Batteries

AGM Batteries are sealed units, with a positive atmosphere. This construction is designed to recombine the gases inside the battery a certain number of times, retarding the need for watering.

However, there are a myriad of ways to hurt this battery, and they all have to do with the charger.

This article is designed to help you to ensure your charging system, and you the owner, are doing everything in your power to safeguard that investment in your new AGM Marine Batteries. We will use the analogy of a closed water tank to describe the system, This way many that have less electrical understanding, can easily grasp the concepts.

A Battery is like a Water tank because each stores something;

Batteries Store Power, Water Tanks Store, Water Each is sealed (AGM especially). And if you put the stuff in too fast, you harm the tank. You put too much in the tank, and it pops. You put the stuff in fast, and it takes less time. The analogies go on, but I bet you get the point.


The first thing to consider is the float voltage.

Once your battery is fully charged, you need to keep the power on it, but not too much. The tank is full. If you put the hose on full blast, you will blow the a battery, you boil out the electrolyte. The float voltage is the voltage for the float mode of the charger, or the 3rd phase of a 3 phase charging regimen. The float charge should keep a battery "tipped up", at 100% charge, for ready deployment to the circuit.

However, should your charger be overcharging the system because it has the wrong float voltage, you are actually overcharging your battery all the time. Check the manufacturer specifications, and ENSURE your float voltages are accurate or you are burning off battery life span every time the thing sits on.


Batteries self discharge at a rate of 2% in the first 24 hours, and another 2% over each ensuing 30 days. This is 8% over 120 days, the longest you should ever leave your batteries unattended anyway.

Based on most battery charger outputs, even the little ones, you will significantly overcharge the batteries should you put them on a trickle charger and leave them, UNLESS it is within the float voltage tolerances.

See the float voltage for that discussion, but should you choose to use a 14.4 volt trickle charger for instance, on an AGM battery bank, you may well significantly overcharge the bank. Think of it like leaving the turkey in the oven on 200 for a week and a half....a bit dry wouldn't you say, lucky if you don't have a fire too...


Your AGM batteries feel the same way, but know they were designed to deal with it better than anything else on the market. If you just put a complete, full, 3-stage, maintenance charge on your batteries that are stored, once every 3-4 months, 3-4 times a year, they should be able to be charged the day you want to go.

By putting a good maintenance charge on your batteries at least once or twice during annual storage, you should be able to use them the following year. OBVIOUSLY, CHARGE YOUR BATTERIES BEFORE YOU LEAVE THE GARAGE. Batteries are a storage tank, not a power generator.


AGM Batteries DO NOT NEED THE EQUALIZER. Turn off equalizer functions on all AGM battery installations to avoid the burning out of the electrolyte.

The Equalizer function on a battery charger is an intentional overcharge, designed to boil a battery. This is done because flooded batteries require the acid inside to be mixed by the boiling action. The acid water mixture inside separates, requiring a boiling to remix it thoroughly, often.

AGM Batteries, due to their construction, do not have this problem, and therefore do not need the equalizer function for routine operation.

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