Batteries for marine use are made with more intensive construction techniques to make them stronger and more resistance to pounding and vibration. The "flooded cell" type, indicating liquid electrolyte, is typically inexpensive and long-lasting, but requires some maintenance. These usually have removable caps that allow for the electrolyte to be tested and maintained. MMF or Marine maintenance Free Batteries are specially designed to recondense any evaporation of electrolyte making them hassle free as they do not require topping up.
Both these types are for starting (cranking) usage so are designed to deliver large bursts of power for a short time, as is needed to start an engine. Once the engine is started, the battery is recharged by the engine-driven charging system. Starting batteries are intended to have a low depth of discharge on each use. They are constructed of many thin plates with thin separators between the plates however their design does allow for some shallow cycling.
More costly alternatives to flooded batteries are "valve regulated lead acid" (VRLA) batteries, also called "sealed" batteries. These are usually AGM (absorbed glass mat) type construction that makes them spill proof and provides good cyclic ability.
Deep cycle batteries are also used extensively in marine uses particularly in house bank and these should be used in place of marine starting batteries for deep cyclic or house bank use. These may be referenced in the Deep Cycle section under MDC Marine Deep Cycle.
