Marine batteries are lead acid batteries that come in two main types: Starting and Deep Cycle batteries.
What is a Starting Marine Battery?
A starting (cranking) marine battery is designed to start the engine of the boat. Outboard motors are better started with a starting marine battery. Starting marine batteries have thinner plates and should not be used for deep cycle applications, thinner plates are prone to warping and pitting when discharged. Engine cranking requires a lot of power in a short time. A general rule of thumb when buying a marine battery is “the bigger the battery, the higher the cranking power”.
The marine cranking amp (MCA) or cranking amp (CA), is found on the marine battery label. It measures the marine battery’s starting power.
A deep cycle marine battery is designed to be regularly deeply discharged using most of its capacity, unlike most automotive batteries, a car battery just starts the engine then the alternator takes over . A deep cycle battery is designed to discharge between 45% to 75%. They have thicker plates and can last numerous discharge cycles. Trolling motors and other boating accessories that use a little bit of power over an extended period need a deep cycle marine battery.
Look for the deep cycle marine battery’s reserve capacity (RC). The higher the RC number, the longer the battery will power your boat accessories. Check your boat or trolling motor’s owner’s manual to see how much RC is recommended. Getting a marine battery with the highest RC possible is a good idea. Not having enough could leave you stranded on the water.
What is an AGM Marine Battery?
AGM is short for “absorbed glass mat,” these batteries have a fiberglass mesh between the battery plates that contain the electrolyte. AGM batteries make great deep cycle batteries. They deliver better performance if they are recharged before they drop below the 50% discharge rate. AGM batteries are safer to use and safe for the environment because they are leak proof, have two times as long to discharge, and they have a longer lifespan.