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Power Fishing: AGM Batteries...Don't Leave Home Without Them!


Anglers demand high performance from their boats, outboard, trolling motors down to their rods, reels and hooks!  And, they’re willing to pay for it!  Bass rigs run well into the $40,000 range!  Even lures are pricey with some Japanese lures going for $80 on EBAY!  The fishing industry accommodates this appetite for techno fishing! And now it’s the battery’s turn!

Batteries have been around for a very long time including the first one, discovered in Baghdad ruins, dating back to 250 BC. But, the guy credited with being the inventor of the modern battery is Italy’s Alessandro Volta, giving name to the “volt”. In electrical terms a battery is an electrochemical device that converts chemical energy into electricity.  Batteries store electricity, they don’t make it, for future use. Starting batteries deliver a burst of electricity for a short period of time and recharge once the engine runs. When starting batteries fail they can’t start engines. The other battery in a bass boat is the deep-cycle, providing a steady stream of power to run trolling motors. Deep cycle batteries undergo the same deterioration over time as starting batteries.

Deep cycle battery life varies with use, maintenance, charging, temperature, and other factors including overcharging death. Allowing batteries to sit for extended periods of time can also be dead on arrival when called into service. Typical expectations for deep cycle batteries:

    * Starting: 3-12 months

    * Marine: 1-6 years

    * Gelled deep cycle: 2-5 years

    * AGM deep cycle: 4-7 years

Batteries are not 100% efficient, losing energy through heat and chemical reactions when charging and discharging resulting in a decline in capacity. Most charging and discharging loss is due to internal resistance generating heat, as batteries get warm when charged.  Lower internal resistance allows batteries to last longer. Even fully charged batteries hold less energy over time, until unable to store enough energy to make it through a day of fishing. Shopping for batteries might leave you short charged. It’s impossible to determine what you’re really buying. Battery quality and construction can vary from cheap off-brands with thin plates to true deep cycle brands, such as Deka. Thin positive plates, eaten away gradually, rank among the top 3 reasons for battery failure. Thicker plates lead to longer life. You get what you pay for.

When will batteries fail? Voltmeters indicate condition, but can show a perfect 12-volt battery reading that won’t start engines.  A new device, the Battery Bug Starting Battery Monitor (SBM) tests batteries every start, tracking battery decline, alerting when batteries approach the end of life with a “fuel gauge” display. For deep cycle batteries, the Argus Battery Bug Deep Cycle Monitor (DCM) continuously monitors the battery’s internal resistance, indicating battery health more accurately than voltage readings. A display and audible alarm indicates when batteries need to be recharged. It also tracks the battery’s deterioration alerting the user when the battery needs to be replaced.

If a battery has removable caps, as do standard batteries, there will likely come a time when they’ll have to be topped off with water. Even so-called “maintenance-free” batteries need to be filled over time. These “old fashioned” batteries come with warranties, not much help when continually replacing them or when they die on the water. Battery makers know batteries will fail and warranties take some of the consumer sting out of down time. Batteries, bass fishing’s ugly stepsister, have been locked away in the dark bilges of the boat, exhumed only upon failure!  Basic bass boat batteries rely on 1850’s technology. Emails sent around the world in seconds, cars adjusting braking, steering and deploying safety equipment, and over 100 stations on our televisions, but what’s happened to the lowly deep cycle battery?  A lot!

"Gel Cells" contain a "gelled" acid.  The addition of Silica Gel turns acid into a solid mass that looks like gooey Jell-O and is impossible to spill even if broken. However, they must be charged at a slower rate to prevent excess gas from damaging cells. Fast charging on a conventional automotive charger may permanently damage them. Gelled batteries are sealed, utilizing a tiny valve to keep slight positive pressure. Absorbed Glass Mat batteries (AGM) cannot be filled and are sealed valve regulated. Newer AGM batteries have all the advantages of gelled, with none of the disadvantages. AGM sealed battery technology was originally developed in 1985 for military aircraft where power, weight, safety, and reliability were essential considerations.

AGM sealed batteries use a very fine fiber Boron-Silicate glass mat between the plates but can take much more abuse than gel cells. In addition, since there’s no liquid to freeze and expand, they are practically immune from freezing damage.  AGM’s are also "starved electrolyte", as the mat is about 95% saturated rather than fully soaked, meaning they will not leak acid even if broken. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery. This also means they’re non-hazardous and shipping costs are lower.  AGM’s are about the same cost as gelled.

Nearly all AGM batteries are "recombinant"; Oxygen and Hydrogen recombine INSIDE the battery. Recombining is typically 99+% efficient, so almost no water is lost.  The charging voltages are the same as for any standard battery so there’s no need for any special adjustments or problems with incompatible chargers or charge controls. Furthermore, the internal resistance is extremely low, creating almost no heating of the battery even under heavy charge and discharge currents.

One of the biggest killers of batteries is sitting stored in a partly discharged state for a few months. A "float" charge should be maintained on batteries especially if not used. AGM's can sit in the off-season or between trips for much longer periods without charging than standard batteries. AGM’s have a very low self-discharge, 1% to 3% per month is usual. Discharge rates for “standard” batteries can be up to 15%! If left for longer periods, all batteries should be trickle charged to avoid damage from sulfation. A battery can meet tests for being at full charge, yet be much lower than it's original capacity. If plates are damaged, sulfated, or partially gone from long use, the battery may give the appearance of being fully charged, but in reality may go dead very quickly under load. This same thing can occur in gelled cells if overcharged and gaps or bubbles occur in the gel. Temperature compensation on chargers, like the Minn Kota on-board chargers, work well if the charger is subject to the same temperatures as the batteries. This is very important when batteries self discharge.

Keeping batteries charged increases life. Resistance in a battery makes it harder to charge. Lead-acid batteries charge to 85-95% while deep cycle AGM's (such as Deka) can approach 98%. Bottom line…AGM’s charge faster and fuller!  Most battery chargers are bulk charge only, and have little voltage regulation, fine for a quick low battery boost but not for long periods. Voltage regulated chargers, such as Minn Kota’s MK 345 On-Board Charger, deliver rapid recharging and fully automatic 3-stage charging (bulk, absorption and maintenance) operation to provide a full charge every time and weighs only 22 pounds. Minn Kota offers automatic temperature compensation delivering fast charging recovery, even in extreme temperatures, while protecting batteries from overcharging. The MK 345 Kota is waterproof, shock and vibration-resistant, with short circuit, reverse polarity and ignition protection.  Recommended with 12V/6-cell batteries (50-130 amp hour rating) that are flooded/wet cell, maintenance free or starved electrolyte (AGM) only. Vent caps on flooded batteries should remain on the battery while charging to prevent water loss and splashing that may occur when bubbling.

As batteries age, their capacity decreases and maintenance requirements increase; longer charging time and/or higher finish rate (higher amperage at the end of the charge) and they need to be watered more often. Never add acid to a battery except to replace spilled liquid. Add water after charging unless plates are exposed, then just enough distilled or de-ionized water to cover the plates. After a full charge, the water level should be even in all cells and usually 1/4" to 1/2" below the bottom of the fill well in the cell (depends on battery size and type). Only clean water should be used for cleaning the outside of batteries. Solvents or spray cleaners should not be used.

Whether it’s a 24 or 36 volt trolling motor system, replacement batteries should be the same size, type and manufacturer (if possible). Also keep the age and usage level similar. Do not put a new battery with others more than 6 months old. Either replace with all new or use a good used battery. It’s a bad idea to buy new batteries and "save" them for later. By the way, Lead-Acid batteries do NOT have a memory, and the rumor they should be fully discharged to avoid this "memory" is totally false and will lead to early battery failure. The most efficient way to charge a battery is to do it slowly! There’s no truth to the myth about not storing batteries on concrete floors. Around for 100 years dating back when battery cases were made of wood and asphalt. Acid leaked, forming a slow-discharging circuit through the now acid-soaked and conductive floor.

Since 1946, East Penn Manufacturing has been making thousands of different sizes and types of lead-acid batteries, and battery accessories for virtually any application. The world’s largest and most modern single-site manufacturing facilities have contributed to their reputation for world-class quality products. For over fifty years East Penn’s made in the U.S.A. Deka batteries have set the standard for the absolute highest quality and most reliable performance in the industry, earning a spot on Fortune magazines “100 Best Companies to Work for”. Many modern motorcycles utilize AGM batteries. NASCAR, IHRA, SCORE, and other top racing leagues are continually equipping Deka AGM products in their vehicles. The switch is on due in large part to the fact these batteries are vibration resistant. Bass boat owners are also seeing the benefits!  If your current batteries are leaving you without a charge, then be in charge with a switch to AGM batteries.

Steve Chaconas is a Potomac bass fishing guide and BoatUS “Ask the Expert” ( To book a trip or purchase gift certificates:

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