Trolling Motor Battery Technology The Pros Use

By Capt. Steve Chaconas

A look at the different types of trolling motor batteries used by fishing pros.

Photo of a trolling motor battery

Anglers demand high performance from their boats to their batteries! And, they're willing to pay for it! Bass rigs run well into the $50,000+ range! Pricey Japanese lures go for $80 on EBAY! The fishing industry accommodates this appetite for techno fishing! And now it's the battery's turn!

Battery Types

Batteries store electricity, they don't create it. 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 bass boat battery, the deep-cycle, provides a steady stream of power to run trolling motors. Batteries undergo deterioration over time.

Deep cycle battery life varies with use, maintenance, charging, temperature, and other factors including overcharging death. Batteries sitting for extended periods 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, not 100% efficient, lose energy through heat and chemical reactions when charging and discharging resulting in a decline in capacity. Losses are 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. Voltmeters indicate condition, but can show a perfect 12-volt battery reading that won't start engines. Battery shopping might leave you short-charged as quality and construction varies. Thin positive plates, eaten away gradually, rank among the top 3 reasons for battery failure. Thicker plates equal longer life. You get what you pay for.

Basic bass boat batteries rely on 1850's technology. If a battery has removable caps, they'll have to be topped off with water. Even so-called "maintenance-free" batteries need to be filled over time. "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!

Gel Cell Batteries

"Gel Cell" batteries 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. Sealed gelled batteries utilize tiny valves to maintain slight positive pressure.

AGM Batteries

Pro anglers are switching to Absorbed Glass Mat (AGM) batteries. They can't be filled and are sealed valve regulated. AGM batteries have gel's advantages without the disadvantages. Originally developed in 1985 for military aircraft, where power, weight, safety, and reliability were essential considerations, AGM technology utilizes tightly packed and rigidly mounted Boron-Silicate glass mats between plates to absorb more abuse than gel cells. With no liquid to freeze and expand, they're practically immune from freezing damage.

AGMs are also "starved electrolyte", as the mat is about 95% saturated rather than fully soaked, they won't leak acid even if broken. Withstanding shock and vibration better than standard batteries means they're non-hazardous and shipping costs are lower. AGMs cost about the same as "gels".

Sitting stored in a partly discharged state for a few months is the biggest battery killer. A "float" charge should be maintained on idled batteries. AGMs survive off-season or in-between trips much longer without charging than standard batteries. If left for longer periods, all batteries should be trickle-charged to avoid damage. Sulfated plates may give batteries the appearance of being fully charged, but in reality may go dead very quickly under load. With a low self-discharge, 1% to 3% per month, AGMs are much lower than (up to 15%) "standard" batteries!

AGM's Charger Faster

Charging voltages of AGMs are the same as standard batteries so there's no need for special adjustments or problems with incompatible chargers that gels create. Internal resistance is extremely low, creating almost no battery heating even under heavy charge and discharge currents. Lead-acid batteries charge to 85-95% while deep cycle AGMs approach 98%. Bottom line — AGMs charge faster and fuller! However, 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 MinnKota'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. MinnKota offers automatic temperature compensation delivering fast charging recovery, even in extreme temperatures, while protecting batteries from overcharging.

Unlike AGMs, wet batteries do not age gracefully. Capacity decreases and maintenance requirements increase. They require longer charging time and/or higher finish rate (higher amperage at the end of the charge) and they need to be watered more often.

Charging Flooded Batteries

When charging flooded batteries, vent caps should remain on while charging to prevent water loss and splashing. 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.

Replacing Batteries

For all batteries, 24 or 36 volt trolling motor systems, replacements should be the same size, type and manufacturer (if possible). Also keep the age and usage level similar. Don't put new batteries 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.

Rumors And Myths

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, dating back when battery cases were made of wood and asphalt, about avoiding storage of batteries on concrete floors. Acid leaked, forming a slow-discharging circuit through the now acid-soaked and conductive floor.

Since 1946, East Penn Manufacturing (DEKA) has been making thousands of different sizes and types of lead-acid batteries, and battery accessories for virtually any application. Many modern motorcycles utilize AGM batteries. NASCAR, IHRA, SCORE, and other top racing leagues are continually equipping Deka AGM products in their vehicles. In the past 2 years, many bass boat owners have been switching to AGMs; they are vibration resistant, charge quicker and fully, and last longer! If your current batteries are leaving you without a charge, then be in charge with a switch to AGM batteries.