Re: Auto Battery Or Marine Battery
Cut/ pasted from Google:
The names "auto" (or automotive) and "marine" primarily give marketing information for batteries rather than specifications for use. Both cars and a speed boats need a battery to start, but the alternator provides the electricity while running. Some pleasure boats run more like RVs, cruising for a while, but often continuing to use electrical power when stopped. So, in some cases, automotive and marine batteries are interchangeable.
Basic Battery Design
Four basic types of battery designs need to be considered, and all are determined by the thickness of the lead plates. Thin plates are less expensive and provide higher cranking power. More expensive batteries with thicker plates have reduced cranking power, but will run longer. The thicker the plates, the more the battery can be discharged without damage. By rule of thumb, "auto" batteries have the thinnest plates, and expensive (and heavier) "deep cycle" industrial batteries have the thickest plates. "Marine" and "hybrid" batteries have plate thicknesses somewhere in the middle.
Automotive Batteries
Generally speaking, an automotive battery with thinner plates will have a higher cranking power. A higher power automotive battery has larger, but not thicker plates, and will have more cranking power than smaller plates of the same thickness. But either can be discharged only about 5 percent before needing a charge. An automotive battery advertised as an RV battery may have thicker plates and therefore a longer reserve capacity, but may be constructed exactly the same as a battery designated "marine."
Marine Batteries
A marine battery usually will have thicker plates that an auto battery and therefore less cranking power, but longer reserve capacity. A higher power marine battery has larger, but not thicker plates, and will have a longer reserve capacity. A typical marine battery can be discharged to 20 percent. Batteries with even thicker plates may be labeled "hybrid" or "deep-cycle" marine batteries and can be discharged to 50 percent before needing a charge. These may be constructed exactly the same as some batteries designated "RV."
The Marine Problem
To quote David Pasco in "Boat Battery Basics," an Internet information site, "The usual reason why boat batteries are dead is due to having the wrong type, size or quality to meet the vessel's demands. Truly good batteries are expensive and there are few boat builders that provide good batteries with new vessels; usually the quality is minimal, the amount of power inadequate, and the type ill-suited." So even in a new boat with a new battery, upgrading to a higher-quality battery may be the best option.
Battery Specifications
Ampere hour rating is the most common specification and is calculated by multiplying the current in amperes by the time in hours that the current will flow. Cold cranking amperage (CCA) indicates the maximum starting current the battery will provide for 30 seconds at 0 degrees F. Reserve capacity tells how long the battery will put out 25 amps before needing a charge. These specifications apply to all batteries designated either automotive or marine and should be used to determine how a battery best serves its intended purpose.
Conclusions
For a speedboat with a 400-cubic-inch engine in Minnesota, the best choice could be an auto battery with a high CCA. For an RV going on a camping trip, using lights and music all night, or for a pleasure boat with the same plans, either a marine or an RV battery with a higher AH rating and longer reserve capacity would be the best bet. Or, for those who can afford it, a much heavier deep cycle industrial battery can discharge right down to 80 percent before the lights start to dim.
