Flooded vs AGM Batteries

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Flooded vs. AGM Batteries

By: Battery Systems – Eric Wasson


Wet Cell, Lead-Acid batteries are the traditional option – they are called “flooded” batteries. These have a plastic case that has vertical lead and lead oxide plates inside. Battery acid fills the space in between those plates. The reaction between the lead, lead oxide, and battery acid creates an electrical current.

AGM (absorbed glass mat) batteries function in a similar way, however they have one important design difference.  AGM batteries have glass fibers woven into sheets that are put in between the plates of the battery. These plates are then soaked with battery acid. Rather than having acid sluicing around inside the battery, the acid soaked plates suspend the solution, and remain in contact with the plates at all times.


This design difference makes the AGM far more efficient. It has a cycle life that is nearly two times as long, a recharge time cut in half, and can absorb twenty times the vibration resistance. Furthermore, this makes AGM batteries spill-proof and allows shipment of the batteries without hazardous material restrictions.  

There are four, distinct, technical advantages of an absorbed glass-mat battery versus a flooded lead-acid battery:

1. AGM batteries do not show terminal corrosion. Without terminal corrosion the battery needs less lifetime maintenance.

2. The AGM battery neither produces nor expels hydrogen or oxygen gases like the flooded lead-acid battery does. Without these external gasses escaping during charging and discharging, electrolyte and water loss is avoided.

3. When comparing batteries in the same group size, AGM’s permit additional plate surface area. An increased plate surface area directly correlates to higher ratings in cold cranking amps (CCA) and reserve capacity (RC).

4. An AGM battery has a lower internal resistance than a flooded lead-acid battery. This allows faster recharge and a slower discharge.

In practical use, this difference has a few key applicable advantages.

1. Cold Weather: the increased CCA of AGM’s allows automotive batteries to start easier in cold weather. This means you have a better chance of batteries starting- avoiding being stranded due to a battery that is either dead or won’t turn the engine over in subfreezing temperatures.

2. Marine applications: deep-cycle AGM’s excel for marine applications. AGM’s allow a slower battery drain and faster charge- components important for batteries used for trolling motors and on-board electronics.

3. Extreme Applications: AGM’s are better than flooded for applications with lots of stopping and starting, like mail carrier vehicles, construction vehicles, and delivery trucks.

4. Construction, Powersports, Off-Road, Farming: The incredible vibration resistance of AGM’s makes them the ideal choice for vehicles that operate in bumpier conditions.

Centennial Battery, as well as other battery companies we sell at Battery Systems offer flooded and AGM batteries for purchase.

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