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What’s Inside Your Marine Batteries

April 19th, 2012 by
A Portrait of Thomas Jefferson as Secretary of...

All quotes are not created equal. (Photo credit: Wikipedia)

Once you’ve decided which kind of marine battery you need (cranking, deep-cycle or dual-purpose), the next decision is battery chemistry. To misquote Thomas Jefferson, “not all chemistries are created equal.” The three different battery compositions – wet cell, absorbed glass-mat, and gel – have different advantages.

Wet Cell Marine Batteries

Often referred to as flooded cells, wet cells are the most popular marine batteries due to price, discharge and recharge cycle capabilities and weight. In addition, you are less likely to damage them by overcharging. Incidentally, this battery chemistry can have the highest self-discharge rate of the three chemistries, about 6%-7% a month.

Almost sunken boat.

That’s not the kind of wet we’re talking about. (Photo credit: Wikipedia)

Unfortunately, these cells require more maintenance than the other battery types. These batteries need to be regularly inspected and topped off with distilled water. Fortunately, vent caps make this process easy. Anyone with a battery hydrometer and five minutes can maximize the life of their wet cell marine battery.

Of course, wet cell batteries must be stored upright to minimize the risk of spilling electrolyte. Just be sure not to rock the boat.


AGM Marine Batteries

If you need a battery that is more shock- and vibration-resistant, try an absorbed glass-mat (AGM) battery. Inside an AGM battery, a dense mat is saturated with the battery’s electrolyte (a mixture of acid and water.)

Unlike wet cells, AGM cells require no maintenance, except for periodic cleaning of the positive and negative terminals. AGM cells are also sealed, which eliminates the possibility of acid and flammable gases from being released into the atmosphere. Additionally, the AGM design means this battery can be installed at any angle, are shock- and vibration-resistant and have a low self-discharge rate of 3% per month.

Just be careful recharging this bad boy. If accidentally overcharged, no amount of water can rehydrate this sealed battery.

Gel Marine Batteries

Now, gel-based marine batteries have liquid electrolytes gelled with silicates. Like the AGM, gel batteries are sealed, shock- and vibration-resistant, and there’s no need to add water. Going a step beyond AGM, these batteries resist overcharging and can handle extremely low temperatures. Combine that with some long cycle life and a low self-discharge rate (less than 1% per month), these gel batteries make the best option for boaters who tend to forget to charge their batteries before and after the season.

Learn about the Interstate Batteries ECL Professional series of marine/RV batteries.

Learn about the Interstate Batteries ECL Professional series of marine/RV batteries.

On the downside, the gel batteries tend to have a higher price. They’ll also need a specific gel battery charger.

Now you know what’s inside the different marine batteries, let’s get you outside. Pick up an Interstate battery at your nearest dealer or visit for more info on our newest line of marine/RV batteries, the ECL Professional Series – whichever floats your boat.


By Kristi Rau (3 Posts)

Posted in Marine, Tips
Tags: , , , , , , , , , ,



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About The Outrageously Dependable Blog

Interstate Batteries® sells more than 16,000 kinds of batteries—from AA alkalines and automotive batteries to critical power solutions, and everything in between. Combine professional battery services, recycling programs and the largest battery distribution network in North America, and you’ll find Interstate has EVERY BATTERY FOR EVERY NEED®. Learn more about Interstate Batteries or shop online!

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