The first thing to remember when talking about marine batteries -- batteries for your yacht or boat -- is that there are two main types of such batteries, serving two separate purposes. The first one, called "cranking batteries," is the one used for starting the main engine, while the second one, "deep cycle," are meant for trolling motors.
Here's where the main differences lie. Cranking batteries, the ones intended for the main engine, contain a number of thin lead plates giving better bursts of energy, which is needed for a quick start. Deep-cycle batteries, used for trolling motors, come with fewer but thicker plates, whose purpose is providing better power-output for a longer period. The thicker plates also do a better job in withstanding higher temperatures, which the motor will encounter when heavy current is drawn down for an extended run-time.
While they're both batteries seemingly serving similar purposes, never use them interchangeably. Each of those two types are designed differently, and utilizing a cranking battery, for instance, for a deep cycle might result in quickly overheating.
Batteries use lead-plates, which are separated from each-other by spacers, immersed in electrolyte. Using a battery generates heat, dissipating the water and exposing the lead-plates. Left exposed, causes the lead-plates to overheat and warp, so keeping the battery "wet" is pretty important. Avoid using tap-water, as the contaminants it contains could harm your battery. Stick to distilled water instead.
A good, though expensive alternative, that will help avoid most of the potential trouble, is a gel battery. Contrary to wet-cell batteries, gel batteries are not as prone to sulfur buildup. Gel batteries are also sealed, so they won't spill acid if tipped over or sloshed by waves. Gels are also safer in the sense that they won't explode, as will lead-acid batteries under certain conditions. so, while the average price for a gel-battery could be as much as double than wet-cells, the benefits outway the cost.
Another thing to remember has to do with discharging the battery. Discharging tends to cause sulfur to deposit on the lead-plates, which will dissolve back into the electrolyte when the battery will be recharged, and this can shorten the battery's life. Which is why promptly recharging the batteries after use as well as checking water-levels after use are important things to remember.
When it comes to marine batteries, the choices get even more diversified and difficult to decipher. The most common terms you'll encounter are words and phrases such as "Spiral-Cell Orbital Plate Technology," "Advanced High Power Density Technology," MCA@32° (Marine Cranking Amps at 32 degrees Fahrenheit), CCA@0° (Cold Cranking Amps at 0 degrees Fahrenheit), and Ah (Ampere-hour rating). Let's look into them in a bit more detail.
First off, the reason this temperature is used for rating-standards is that batteries are at their lowest ebb under really cold conditions, making it the best way for establishing a common reference point. Batteries with high ratings under the worst conditions perform even better during moderate or ideal conditions.
The Marine Cranking Ampere (MCA) rating deals with the number of amperes a battery can support for 30 seconds at a temperature of 32°F until the battery voltage drops to 1.20 volts per cell, or 7.20 volts for a 12V battery. Thus, a 12V battery that carries a MCA rating of 600 CCA tells us that the battery will provide 600 amperes for 30 seconds at 32°F before the voltage falls to 7.20V.
Cold-Cranking Amperage (CCA) is a measurement of the number of amps a battery can deliver at 0° F for 30 seconds without dropping below 7.2 volts. The value of CCA will change with battery temperature -- CCA increasing with higher temperatures.
The Ampere-hour (Ah) rating, usually found on deep-cycle batteries, defines the capacity of a battery. A typical battery that is rated as a 100Ah battery, at the 10 hour rate of discharge, is capable of delivering 10A for 10 hours before the terminal voltage drops to a standard value such as 1.67 volts per cell, or 10.02 volts for a 12V battery. Similarly, a 50Ah battery would supply a 5A load for 10 hours.
The best way for going about shopping and selecting batteries for your boat is to determine first on the amount of money you're willing to spend, and then setting out on finding the ones fitting your budget. Compare and contrast the features and ratings, with prime emphasis given to MCA, CCA and Ah.
As always, feel free to reach out to us with any questions!