By Gregg NestorThe battery on board a trailersailer is the closest thing to an aquatic indentured servant as one can find. It is often forgotten and forced to spend most of its life in some dark, cramped, damp, recess of the boat’s bowels. It’s usually cared for poorly and often subsists on meager rations. However, when called upon it is expected to perform unparalleled electrical feats; that is until Mr. Murphy’s Second Law kicks in…
When left to themselves, things always go from bad to worse.Understanding how a marine battery works and responding to its needs goes a long way in nurturing it into healthy old age. It’s not rocket science, but a combination of routine maintenance and proper charging, in other words—care and feeding.
Tech Talk Electrically speaking, marine batteries are technically known as accumulators (storage batteries). They are made up of a series of several ‘secondary’ galvanic cells. Secondary cells can be recharged by passing an electrical current through them, so that their electrodes are regenerated. Cells in which the electrodes cannot be recharged and are consumed during discharge are called ‘primary’ cells. Disposable flashlight batteries are an example of ‘primary’ cells. Typically, the electrodes of a storage battery are comprised of alternating negative (lead) and positive (lead dioxide) electrodes or plates suspended in an electrolyte of dilute sulfuric acid. In operation, the electrodes, together with the electrolyte, convert chemical energy into electrical energy. During this discharge, lead sulfate and water is formed. Recharging reverses this process.
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Types and Kinds Currently, there are three battery chemistries or varieties of marine storage batteries on the market. They are the wet or flooded cell, the gel-cell, and the AGM (absorbed glass mat). The flooded cell, the least expensive of the three, requires periodic inspection and topping off with distilled water; the gel-cell, a sealed no-maintenance battery, is a bit more costly than the flooded cell; and the AGM, another sealed no-maintenance battery, is roughly twice the cost of a comparable flooded cell battery.
There are pro and cons to each—some significant, some moot; however, as long as you purchase a quality product, follow the manufacturer’s maintenance and charging recommendations, and, if you have a multiple battery system, do not mix types—they all will work well.
In addition to the three chemistry types, marine batteries are available in the following configurations: deep cycle, starting, and dual-purpose.
Deep Cycle Batteries are designed with thick electrode plates that enable them to be deeply discharged repeatedly without incurring damage. The combination of one discharge and one recharge is termed a cycle. The number of 100 percent discharge cycles that can be produced over a battery’s life is how the battery’s longevity is measured. Three hundred to 500 cycles are typical. Deep cycle batteries are best suited as ‘house batteries’ that power lights, electronics, and other onboard electrical accessories.
Compared to deep-cycle batteries
, Starting Batteries have a larger number of electrode plates; however the plates are much thinner than those of their deep cycle cousin’s. This greater number of plates affords more surface area for chemical reaction to take place, hence delivering the higher current that is needed to start a motor. Since the plates are structurally weaker, they cannot handle the strain of deep cycle use. A typical starting battery cannot withstand more than a few deep discharges before it fails. The power of a marine starting battery is measured by its MCA (marine cranking amps). MCA is the number of amps a battery can deliver for 30 seconds at 32 degree without the voltage dropping below 7.2 volts. Starting batteries are engineered to supply lots of current (amps) over a short period of time (motor starting).
Dual-Purpose Batteries are part deep-cycle battery and part starting battery rolled into one. Often marketed as a ‘universal’ battery, the dual-purpose battery has its niche. If you motor frequently and your electrical demands are low, a dual-purpose battery is ideal. Also, if you have a bank of two batteries that are used for any and all loads on board, two dual-purpose batteries will provide reliable service. However, a better dual battery system would be comprised of a dedicated starting battery and a dedicated deep cycle ‘house’ battery. (First Mate’s Postulate: Dual-purpose chickens don’t work. If you want eggs, get a layer and if you want meat, get a broiler.) To gauge the relative effectiveness of various dual-purpose batteries, compare the number of deep cycles and the MCAs.
Why Batteries Fail Undercharging: As is the case with most sailboats, the batteries of trailersailers are repeatedly deeply discharged. However, unlike their larger relatives, trailersailers often do not have outboard motors equipped with alternators to recharge their batteries. In fact, in lieu of an alternator, many outboards feature electric starting that exacerbates the battery’s discharge condition. Even if equipped with an alternator, it is often unlikely that the boat’s battery will be recharged to a capacity greater than 65-75 percent. This is mainly due to the fact that sailboats rarely operate their motors for any significant length of time. Since it took a while to discharge the battery, it will take a while to recharge the battery. Recalling how a storage battery works, the uncharged 25-35 percent is in the form of lead sulfate, a relatively soft material. Over a period of time, these lead sulfate crystals, covering the battery’s electrode plates, harden. This process is called sulfation. When this occurs, normal charging cannot result in the chemical reconversion to a charged state. Further undercharging and sulfation leads to further capacity loss and premature aging/battery failure.
Overcharging: Using a battery charger when onshore is often employed as a substitute for the lack of a trailorsailer’s onboard charging capabilities. This technique, if properly done, has its merits. However, if left too long, some battery chargers will overcharge the boat’s battery. This results in loss of electrolyte through evaporation. Also the battery’s positive electrode plates can be irreversibly damaged by excessive chemical reaction. Instead of maintaining a battery at peak charge, persistent overcharging can reduce a battery’s capacity to 50 percent or even less. (Skipper’s Theorem: Just because it takes one pregnant woman nine months to have a baby, doesn’t mean that getting nine pregnant women together will result in a baby in one month.)
Excessive Deep Discharge: During discharge, chemical energy is converted into electrical energy. This is the result of a chemical reaction, which routinely places a stress on the battery. The deeper the discharge, the greater the stress. Every time that the battery is deeply discharged, some of the active material on the electrode plates is sloughed off. Over time, this shed material can build up from the bottom of the battery or even between the plates. The resultant ‘bridging’ shorts out the cell(s) and results in battery failure.
An Ounce of Prevention Treated properly, marine storage batteries will die of old age. Here are a few things that can help in preventing battery failure and prolonging battery life.
Monitor your Battery: Periodically check the battery’s state of charge, with a hydrometer. Water has a specific gravity of 1.0. A fully charged battery will display a specific gravity of 1.270 or more. A specific gravity of 1.150 or less indicates a discharged battery. Be sure to measure all the cells. If you don’t have a hydrometer, use a voltmeter. A fully charged battery will register 13.5volts (if charged from a battery charger) or 14.2 volts (if charged from an alternator). A reading of 12.2 volts indicates a low battery and a reading of 11.2 volts suggests a dead battery.
Good Housekeeping: A clean, cool, and dry battery will give noticeably good performance. Clean the top and sides of the battery with water containing a small amount of detergent. Rinse the cleaned battery with water and dry. Be sure to temporarily plug the vent holes with toothpicks during the ‘bathing’ process. Remove any corrosion products with a thin paste made from baking soda and water. Again, rinse with water and dry. Burnish the battery terminals with a wire brush, coarse steel wool or a terminal cleaner. Lightly coat them with a commercial battery corrosion inhibitor or WD-40. Impregnated felt washers that fit over the battery terminals to prevent corrosion can be found at auto parts stores.
Periodic Feeding: If your battery is not ‘maintenance free,' check the electrolyte level in each cell every month. If any is found to be low, add distilled water to the required level. Rainwater is an acceptable substitute for distilled water. You can avoid making a mess by using a squirt shampoo bottle for topping off your battery cells. I have found that the cells of many ‘no maintenance’ batteries can also be accessed with a little ingenuity (gel-cells and AGM batteries not included).
Proper Housing: Keep your battery in a secure and vented plastic battery case with cover. This will prevent the battery from tipping over and resulting in a short circuit during rough conditions or excessive heel. Also, should the battery area become flooded, the cover will act as a diving bell, keeping air in and water out.
Full Charge: Don’t leave your marine storage battery too long with a partial charge. Over time, sulfation will reduce its capacity. Therefore, periodically bring your battery up to full charge.
Float Charging: If you intend to leave your battery unused for a long period of time, be sure to first fully charge it. It will not remain in a fully charged state. All batteries will self-discharge over time. A flooded-cell battery self-discharges at 6-7 percent per month, while gel-cells and AGMs display a rate of around 3 percent per month. In cold weather, a battery can even freeze if its charge becomes too low. Therefore, during the storage period, periodically recharge or, better yet, float charge (constantly charge at a low level) your battery to keep it from sulfating. A low output ‘trickle’ charger or solar panel having an output no higher than about 13.5 volts works well.Your marine storage battery is one of the most important systems on your trailersailer. Without it, you may not be able to display your lights, call for help, pump your bilge, or maybe even start your auxiliary. However, with a little proper care and feeding your battery should provide you with years of service. But if you use it and abuse it, you may succumb to Murphy’s Revised First Law: If anything can go wrong with a system, it will, and generally at the moment that the system becomes indispensable.
About the author: Almost 30 years ago, Gregg stepped aboard a sailboat for the first time. On this initial cruise, his wife-to-be, Joyce, said, "What a great place to clear the cobwebs from your mind." And so began the two great loves of his life—his first mate, Joyce, and sailing. Four boats, several states and sailing grounds later, Gregg’s fascination with the sport has not diminished. He performs his own maintenance and upgrades and has developed several novel approaches to common sailing dilemmas. He’s an avid ‘Trailer Sailor’ and has authored over 30 related articles. When not sailing or writing about sailing, this rural raconteur runs the family farm. He and Joyce currently sail an O’day 222 named Splash.If you'd like to contribute to Our Readers Write section, please send your submissions to submit@sailnet.com.
