Marine Batteries - Which Are Best?

Wet Cells are the most common lead-acid battery-variety in use nowadays. They offer the most size and design choices and are built for a lot of different uses. In the marine industry, they more often than not are not sealed so the consumer can refill any electrolyte the battery vented while charging the battery. Every cell will feature a grid of lead plates along with an electrolyte based on sulphuric acid. Since the grid is not supported except at the edges, flooded lead-acid batteries are mechanically the weakest batteries. Given that the container is not sealed, great attention 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 created. The USCG requires that wet cell batteries be kept in a spill-proof container.

Gel Cells use a thickening agent to stop the electrolyte. Thus, if the battery box cracks or is breached, the cell will continue to work. Furthermore, the thickening agent prevents stratification by preventing the movement of electrolyte. As Gel cells are sealed and cannot be refilled with electrolyte, controlling the rate of charge is essential or the battery will be ruined in short order.

Absorbed Glass Mat (AGM) batteries are the most recent phase in the evolution of batteries. Instead of using a gel, an AGM uses a fiberglass similar separator to keep the electrolyte in place. The physical attachment between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact resistant lead-acid batteries accessible today. They were originally intended to be used in aircraft.

In essence, an AGM can do anything a Gel-cell can, only better. However, since they are also sealed, charging has to be controlled cautiously or they too can be destroyed quickly.

Gel and Absorbed Glass Mat batteries are relatively recent but are quickly gaining acceptance. There are a number of good reasons to use them:

Gel and Absorbed Glass Mat (AGM) batteries can give out charge at a higher rate than flooded cells. Practically no gassing under ordinary operating circumstances: Unlike wet cells, gel cells and AGMs are sealed and work under pressure to recombine the oxygen and hydrogen created through the charge process back into water. You find AGM batteries on expensive new yachts such as Hinckley, Hans Christian, Viking, Island Packet, and Broward.

The ability to put Gel and AGMs in the bilges (they can even operate under water) also lengthens their lives: For every additional 15 degrees of heat over 77 deg F, battery life (regardless of type) decreased by half. AGMs can work in any orientation (even though you may lose some capacity that way) and even if a container is cracked, an AGM will not leak. This is a trait particularly important to blue water cruisers who may encounter storms - you don't desire to coat the interior of your yacht with sulfuric acid if you ever get bounced around. Proper (heavy duty) battery restraints are a requirement, regardless of battery type. Gel cells and AGMs require no upkeep once the charging system has been properly set up.

The costs of batteries are an issue: - Wet cell 8-D - $150.00 - Gel - 8-D - $250.00 - AGM - 8-D $365.00

So choose the battery you feel is best for you and enjoy your boat.

Mike Dickens, the author, is a live aboard boat owner and owner/Broker of Paradise Yachts in Florida USA. Paradise Yachts offers used quality yachts to customers worldwide. 904/556-9431 Visit the Paradise Yachts website to view our selection of Used Trawlers, Used Motor Yachts, and Used Sailboats for Sale

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