Let’s Talk Marine Batteries…

When should you replace? Which type? Where should they be installed? How should they be secured?

The manufacturers recommended replacement interval for starting and deep cycle wet cell batteries is 24 months. The full life expectancy for either of these is 30 months. I have seen batteries last longer than 30 months but it is more likely they will fail during that 24-30 month time frame.

Marine cranking batteries are designed specifically for use in engine starting applications with capabilities for quick energy release and faster recharging. The typical engine manufacturers rating for a cranking battery is 1000 MCA (marine cranking amps) at 32°F and 800 CCA (cold cranking amps) at 0°F. Cranking batteries come in several sizes and Group 24 is regarded as pretty much standard equipment in the marine world.

When a marine battery is replaced the cables should be cleaned and locking-type nuts installed on the post connections. A shot of Corrosion-X Red protects against corrosion. The battery must be installed in a tray or box that is secured to the deck or compartment floor. A battery being tossed around at higher speeds in rough water is a recipe for disaster. The best location for batteries in most fishing boats is under the console. Stern compartments are least desirable given that they are often consistently damp or wet which can lead to rapid deterioration of electrical components.

Deep cycle batteries, commonly used for trolling motors, are also available in different sizes. Group 24 and Group 27 are most common in marine applications, Group 31 not so common. While Group 31 offers greater reserve capacity, they require more space. Deep cycle batteries are designed for slow release of energy with slower recharge rate to better handle long term draining from trolling motors, live well pumps, etc. The availability of space usually dictates the battery size selected.

Gel cell batteries are also available for cranking and deep cycle applications and are sized the same - Group 24, 27, and 31. Gel cell batteries that combine cranking and deep cycle features are also available. The life expectancy is 36 months and although they cost more, you get what you pay for.

If your boat is equipped with dual cranking batteries and a battery selector switch, you should always crank and run at position 1 or 2 and alternate each day of operation to keep both fully charged. The ALL position should be used only to crank the engine when the batteries are too weak to do it singly. Operating in the ALL position allows only partial charging of the individual batteries and can mask the fact that one may be weak or completely shorted. Never change battery selection with the key on or engine running unless the switch is marked Ignition Protected. When your boat is not in use the battery selector should be set at the OFF position.

Have a great fall season!
Chris Mapp