Comparing the AGM battery vs the Flooded Lead Acid Battery for Marine applications.
First off, either of these batteries will work fine from an operational standpoint. The question comes down to what is your time, boat, and frustration worth?
Flooded Lead Acid Batteries are standard equipment on many manufacturers boats, yachts, and watercraft. However, each is offered with AGM as an upgrade for your convenience.
EACH WILL WORK:
Both AGM and Flooded lead acid batteries are amperage tolerant. AGM and Flooded Lead Acid Batteries are designed to push heavy amperage loads without detrimental effects to the battery. Both AGM and flooded batteries are able to be charged with high output alternators on those motors. These standards, and the battery's ability to cope in this environment make either a solid choice over a GEL battery.
AGM is BETTER!
We have established that either will work on the boat, AGM or Flooded batteries, but let's get into what separates these two types of batteries in actual use. AGM Batteries are maintenance free, whereas flooded batteries and the space around them require much maintenance.
AGM batteries, being sealed, will not bubble acid out while under a charge. This seal also retards 90% of the smell from the chemical reaction. There is no need to add water to the battery cells monthly, nor is there anything you must do to these batteries but charge them. Simply install your AGM batteries, charge them routinely, and forget about them. There is no clean up, no acid, and no watering to keep up with.
Flooded lead acid batteries on the other hand will smell, will excrete a mist of sulfuric acid, and may even bubble over onto their surroundings during charging and discharging. You must add water to compensate for this or the battery plates will be exposed to the air. Plates that are exposed to the air disintegrate. This acid must be cleaned routinely or any metals in the vicinity will also disintegrate. Basically, if you use flooded lead acid batteries, the money you save you are paying yourself to clean up and maintain the system. What is your time worth?
AGM is more efficient.
Based on Peukert's equations, the German scientist who mathematically solved the battery discharge problem, each battery's efficiency can be computed. AGM batteries are generally far more efficient than are flooded lead acid batteries. This is important when determining the cost to charge and discharge the batteries. Generally an AGM battery will give you between 80-90% of the power pushed into the battery, back. On the other hand, flooded lead acid batteries typically have efficiencies in the 40-60% range. The bottom lines here are time and money. Basically you spend more to charge a flooded battery than you do an AGM. This translates to money as generators eat gas, alternators rob horsepower from the engine, and battery chargers eat kilowatts. The real tragedy is that you get less of that power back from the flooded battery than you do with an AGM battery.
AGM self discharge rates are 80% - 99% better.
Batteries, being a chemical equation in flux, are not perfectly stable. A battery will self discharge as it sits. AGM batteries are far more resilient than flooded batteries when it comes to self discharge. The typical AGM battery will discharge 1 to 3% per month, with this rate remaining stable over the life of the battery. Flooded battery models do not fare as well, losing 5-10% per month when new, and up to 20 or 40% per month as they age due to antimony contamination in the negative plates.
This Marine Battery website shows you how to electrically hook up circuits, install batteries, and run wires for your marine application. You as the consumer are assumed to be using this marine battery information site as a reference tool. The marine battery information herein has been checked, but is not warranted.