Batteries and Battery Systems
Deep-Cycle Batteries Cost Over Life of the Battery Battery Type . . . . . . . . . . . . . . . .Cost Formula Wet-cell . . . . . . .90 amp-hours ÷ 2 (50 percent discharge) = 45 amp-hours x 2,650 cycles = 0.0017¢ per amp-hour Gel-cell . . . . . . .86 amp-hours ÷ 2 (50 percent discharge) = 43 amp-hours x 1,400 cycles = 0.0027¢ per amp-hour AGM . . . . . . . . .92 amp-hours ÷ 2 (50 percent discharge) = 46 amp-hours x 3,000 cycles = 0.0014¢ per amp-hour Please keep in mind that these costs are based on charge-cycle numbers that are quite high. In actual use, your cost per amp-hour will probably be much higher. However, on average the findings here are as good for comparison of battery types as any other method. Although they will require more maintenance than other types, conventional wet-cell batteries are still the least expensive of the three types to buy and own over the long haul. AGM batteries offer all the advantages of the gel-cells plus a less-finicky charge cycle. Therefore, in almost all applications, AGMs are a better choice than gel-cells, but as of this printing you’ll still pay a substantial premium for AGMs over wet-cell batteries. AGMs are a particularly good choice for installations where acid spills are a consideration, as with personal watercraft (Jet Skis) and other sport boats, and they are excellent for use on boats that will be left unattended for months at a time.
Which Battery Is Right for You? All but the smallest open boats should have at least two batteries. The starting battery is for starting the engine and needs a lot of cranking capacity to spin a heavy-duty starter motor. The house battery is used to run equipment such as cabin lights, stereos, refrigerators, and electronic equipment that isn’t connected to the engine. The starting battery should be
a heavy-duty marine cranking battery, and the house battery should be a deep-cycle marine battery. One of my boats, a 15-foot dory I use for bay fishing, has a single deep-cycle battery that I use to operate my fish-finder and running lights at night. The engine is a pull-start outboard, so I don’t need a cranking battery. If I had an electric-start engine on this boat, I would consider an additional cranking battery, even for a boat this small. I hate paddling; it just takes too long against a 2-knot tide. My other powerboat, a 25-foot V8-powered walk-around, is set up with a group 27 cranking battery and a group 27 deep-cycle marine battery.
Deep-Cycle versus Cranking Batteries The difference between cranking and deep-cycle batteries is simple. Cranking batteries are designed to provide a burst of cranking power for a short period of time. Once the engine is running, the engine’s alternator will kick in and quickly recharge the battery, replacing the power used to start the engine. Cranking batteries are not designed to be discharged deeply over and over again. You would be lucky to get one season of boating out of a cranking battery used as a deep-cycle house battery. Deep-cycle batteries, on the other hand, are built with heavy and comparatively thick plates and have much more lead in them than cranking batteries. You can actually tell the difference between the two by lifting them. They are designed to be discharged up to 50 percent of capacity and recharged over and over again without sustaining any permanent damage. Because of the heavier and thicker plates used in deep-cycle batteries, they take much longer to reach full charge than cranking batteries. Therefore, they aren’t a good choice for a starting battery, particularly where an engine will be started frequently and run for short periods of time. Deep-cycle batteries are perfect for use as the house battery in cruisers that will be anchored away from shore power for overnight trips or for fishing boats that will be anchored for long periods with the fish-finder, radio, and beer cooler running. Deep-cycle batteries are designed to take abuse, but even these can’t be completely discharged and recharged continually without failing. Thirty percent 69
