There are two basic types of marine batteries, those designed to start your main engine and those engineered specifically for trolling motors. Batteries for starting your motor are referred to, as cranking batteries and trolling batteries are deep-cycle units. These two types are distinguished in their construction by the plates that are deep inside the case.
Cranking batteries have numerous thin lead plates that give better bursts of energy for a fast start. Deep-cycle batteries have fewer, thicker plates that provide better power output over a longer period of time. Thicker plates also withstand the higher temperatures that are created when heavy current is drawn down for an extended run time. Don't substitute a cranking battery for trolling motor use. Their inherent design strength is also their weakness in opposite applications. A cranking battery in a deep cycle application will overheat quickly.
All batteries use lead plates, separated by spacers, immersed in a solution of some type called electrolyte. Traditional lead-acid batteries contain a mixture of approximately 35% sulfuric acid and 65% distilled water. As a battery is used, it generates heat that dissipates the water and exposes the lead plates. Plates that are left exposed are subject to overheating and warping. When plates warp enough to touch adjacent plates you'll be buying a replacement. To avoid the problem of introducing contaminants like chlorine into your battery, never use tap water to top off the fluid in a battery. Distilled water is always the best choice.
Gel cell batteries typically cost about twice as much as wet-cell batteries; however, gels are not as prone to sulfur buildup. Another positive factor for gel cells is safety. Since these batteries are sealed, they won't spill acid when tipped over or sloshed by heavy waves. Also, gels aren't subject to the danger of explosion that is possible under certain conditions with lead-acid batteries.
When a battery is discharged, sulfur deposits form on the lead plates. When the battery is recharged, the sulfur dissolves back into electrolyte. Sulfur oxidizes the plates and can shorten battery life. Also, when sulfur deposits become large enough they can short out the plates and prematurely terminate the battery's useful life. That's why it's important to recharge batteries promptly after use and check water levels frequently, so that the sulfur isn't allowed to form and solidify.
Once you decide which type you need, the choices for marine batteries are many, and the decision is clouded with descriptors such as "Spiral-Cell Orbital Plate Technology" and "Advanced High Power Density Technology". While these may be legitimate marketing descriptors for a particular feature, the issues are two fold; what does this industry jargon mean in practical terms and how does it compare with other manufacturer's features? Other more relative terms you'll need to know are MCA@32° (Marine Cranking Amps at 32 degrees Fahrenheit), CCA@0° (Cold Cranking Amps at 0 degrees Fahrenheit), and Ah (Ampere-hour rating).
You may or may not be doing much cranking at 0° or even 32°F, but the reason this temperature is used for the rating standard is that batteries are at their lowest ebb under really cold conditions, and it's the best way to establish a common reference point. A battery that has high ratings under the worst conditions will perform even better during moderate or ideal conditions.
The Marine Cranking Ampere (MCA) rating refers to 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.
The definition of the Cold-Cranking Amperage (CCA) of an automotive battery is the amount of current a given battery can deliver for 30 seconds at zero (0) degrees F without dropping below a specified cutoff voltage (manufacturer-specific, but usually 10.5 volts). The value of CCA will change with battery temperature, CCA increasing with higher temperatures.
The Ampere-hour (Ah) rating 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.
To simplify your battery decision, determine how much money you're willing to spend and then select the battery that has the highest ratings in these three areas - MCA, CCA and Ah.
Keeping those expensive marine deep-cycle batteries up to snuff doesn't have to be a chore. Avoid totally discharging wet-cell, deep-cycle batteries as well as avoiding quick charges that creates more heat than the more desirable trickle charge. Promptly recharging your batteries immediately after use will extend their life and also avoid the problem of stepping on the foot pedal of your trolling motor and being reminded that you forgot to charge the batteries after the last trip.
With proper safety precautions, explosions should not be an issue with wet-cell batteries. When in use, and especially when being charged, wet-cell batteries should be well ventilated and care should be taken not to introduce a spark into the battery compartment that is not well ventilated. Another good rule to follow when installing or removing batteries is to always connect the positive (red) lead first and disconnect it last when removing a battery. When the negative lead is connected first and then the positive lead, a spark can result and ignite gases in a confined space.
Convenient, on-board smart chargers eliminate the hassle and worry about overcharging and they're not easily removed. A common problem with loose battery chargers is that they often disappear while batteries are being charged overnight, in motel parking lots or even at your home. On-board chargers that are permanently installed can certainly be stolen, but a thief is less likely to take the time when other more mobile options are available. Once you've returned home from a boating trip, you simply plug the charger into a 120-volt outlet and let these smart chargers maintain your batteries without the hassle of personal monitoring.
Cabela's Smart Leg technology monitors each battery, delivering the correct amps at the right time. The Three-Stage Charging Cycle is completely automatic, just plug it in and forget it. With their auto-shutoff feature, they cannot overcharge your battery, and can be left plugged in during winter storage to keep batteries at their peak. Onboard smart chargers are also ideal for winter storage because they monitor your batteries' levels and automatically recharge them before they get dangerously low. Wet cell batteries that have totally lost their charge are subject to freezing, which will separate plates and expand the battery case until, in extreme cases, it bursts. Once a battery's case bursts and sulfuric acid spills out, nothing good can happen, only bad.
With the right trolling motor, batteries and charger on your boat, many of the worries of a day on the water are eliminated and you can concentrate on the most important reason you bought your boat for in the first place - having fun on the water.
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Frank Ross grew up on a lake in Florida, where fishing and hunting were second nature. He has pursued his passion from the jungles of South America to the northern reaches of the Arctic Circle and most points in between. With a background in newspapers, the wire services and magazines that began in 1970, Frank brings a unique perspective to his work with Cabela's. He is an award-winning photographer with a flair for getting to the bottom line of every story.