The type of battery most utilized in the boating community remains the wet-celled lead acid battery. Using an electrolyte consisting of sulfuric acid, these cells can store large amounts of electrical energy in a relatively little space. This energy is stored within lead grids mounted inside the battery. The lead is what makes wet-celled batteries so heavy.
The battery selection is further divided along the lines of battery construction. Presently, there are three common battery technologies: Wet-cell, Gel, and AGM.
As we stated earlier, wet-celled technology is the most commonly used battery. They offer the most size choices, are the cheapest and can be found almost anyplace. In the marine business, they usually are not sealed so the user can replenish any electrolyte the battery vented while charging the battery. Each cell will feature a grid of lead plates along with an electrolyte based on sulfuric acid. The grids in wet-celled batteries are only supported along the edges, hence these are the weakest mechanically. Since the container is not sealed, great care has to be taken to ensure that the electrolyte does not come into contact with you (burns!) or seawater (chlorine gas!), or an explosion from the hydrogen produced. Batteries should always be stored in a spill-proof box.
Gel Cells use a thickening agent to immobilize the electrolyte. So if the container is cracked, the cell will continue to perform as normal. In addition, the thickening agent prevents stratification by forestalling the electrolyte from sloshing around. Gel cell are sealed and cannot be re-filled so controlling the rate of charge is crucial. Over charging will ruin them in short order.
Absorbed Glass Mat (AGM) batteries are the latest step in the development of batteries. Instead of using a gel, an AGM uses a fiberglass like separator to hold the electrolyte in place. The physical bond between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact tolerant lead-acid batteries available today. These batteries got their start in the aircraft industry
An AGM battery can do anything a gel-cell can do, but only better. However, since they are also sealed, charging has to be controlled cautiously or they too can be ruined in short order.
Absorbed Glass Mat batteries are relatively new but are quickly winning acceptance. Here are a few good reasons to consider them:
1 - AGM batteries can dispense a charge at a higher rate than wet-celled batteries.
2 - No gassing under normal circumstances: AGM batteries are sealed under pressure to recombine oxygen and hydrogen into water during the charging process. Some of your high-end yacht builders use AGMs in their boats like Broward and Viking.
The ability to put AGMs in the bilges (they can even function under water) also lengthens their lives; Remember that for every 15 degrees over 77F, a battery's life will be cut in half
AGM batteries will even function upside down and even if a container is broken, it will not leak. This should be of particular importance to blue-water cruisers that could find themselves bounced around; you would not want sulfuric acid in your boat. Appropriate (heavy duty) battery restraints are a must, irrespective of battery type.
AGMs require no maintenance once the charging system has been properly set up.
The costs of batteries are an issue:
Let's compare prices
- Wet cell 8-D - $150.00
- Gel - 8-D - $250.00
- AGM - 8-D $365.00 (Marine centers have them for $501.00)
So choose the battery you feel is best for you and have fun with your boat.
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