How to Select the Right Trolling Motor Battery

Choosing the best batteries to power your marine accessories can be one of the most daunting experiences in boating. With so many options available it can be easy to end up confused by manufacturer recommendations, specifications, and what really matters in battery selection.

Here, we’ll outline how to select the best trolling motor batteries for your boat in easy-to-understand terms so you can get out on the water with confidence.

Marine Battery Types for Trolling Motors

The first thing you’ll notice when selecting batteries is how many options are available and what the benefits and drawbacks of each might be.  The Three most common marine batteries you’ll find are Flooded Lead Acid (sometimes called wet-cell), AGM or absorbed glass mat, and Lithium Iron Phosphate (LiFePO4).

Flooded Lead-Acid

In one way or another, all batteries use a chemical reaction to create electrical energy. The oldest and most common example of this is the flooded lead-acid battery.  As the name implies, lead plates are housed within this battery and are submerged in acid (sometimes called electrolyte).

These batteries are easily the most common -and least expensive- of all the battery options.  They are easily found in big-box retailers and the less expensive options can readily be found for around $100 or less.

You can expect a battery like this to last a minimum of 2-3 years, which can be extended by maintaining electrolyte (acid) levels with distilled water and using a Minn Kota Precision charger’s deep equalization mode to combat sulfation.

AGM (Absorbed Glass-Mat) 

In recent years the comparative cost of AGM batteries has come down quite a bit, but they will still end up costing as much as twice what a flooded lead-acid battery of the same group size will. The defining feature of AGM batteries is that they are completely sealed and instead of liquid acid, the electrolyte used in AGM batteries is “absorbed” into mats that contact the plates within. This makes them comparatively easier to transport without the risk of spills.

From a weight perspective, AGM batteries are roughly on par with flooded lead-acid options, if not slightly heavier.

AGM Batteries are commonly called “maintenance-free” batteries as their sealed nature prevents the need to maintain the acid level within them. They also tend to last slightly longer than Flooded Lead-Acid batteries if properly maintained because of the lower likelihood of falling victim to sulfation. AGM batteries, however, have the potential to be more permanently affected after being drained completely than lead-acid batteries.

Lithium Iron Phosphate

If you’ve been in the market for new trolling motor batteries recently you may have noticed some changes to what’s available in the market. Lithium Iron Phosphate (LiFePO4) marine batteries are becoming a more common option for powering trolling motors, fish finders, and other accessories.

Lithium marine batteries are by far the most expensive option of the three common battery types, but as more and more manufacturers introduce Lithium options the price of these battery types will continue to fall. 

If you plan to keep your boat and trolling motor system long-term, Lithium could prove to be a smart investment. With some manufacturers offering up to 10-year warranties the total cost of ownership may come out to be a wash vs. re-buying flooded batteries in the same time period.

While still out of the price range of most budget-conscious anglers, Lithium boat batteries’ main advantage is a significant reduction in weight from the other battery types, which can help make your boat more nimble, get out of the hole quicker, and modestly increase top-end speed. These battery types are also known for their ability to output higher voltage levels over long periods of time and have the potential to last several years longer than traditional battery types. 

Anglers may have a hard time determining the compatibility of their trolling motors and chargers with Lithium batteries, so it’s important to note that all Minn Kota Trolling motors and chargers are compatible with 12 volt Lithium (LiFePO4) marine batteries

Deep Cycle Marine Batteries

It’s important to note that no matter what battery type you choose, you’ll want to make sure you find a “deep cycle” battery. This will be clearly labeled and all it really means is that the battery was designed for using smaller amounts of energy over longer periods of time.

The alternative to a deep cycle will be a common cranking battery – these are designed to use a lot of power all at once, like when you power the starter to turn over the engine of your car. These Battery types are also commonly found in marine applications but are generally used to start outboard engines and power auxiliary accessories.

“Deep Cycle” isn’t terminology you will always find when shopping for Lithium marine batteries, but essentially all LiFePO4 batteries are designed to operate this way.

Can I use a Dual Purpose Marine Battery for my Trolling Motor?

Another battery type you may find during your search is a hybrid cranking/deep cycle battery commonly referred to as a “Dual Purpose” or “Dual Purpose Deep Cycle” battery. You may wonder if these battery types are suitable for use with your trolling motor, and the short answer is yes.

Dual purpose batteries have both the reserve capacity to power accessories long-term as well as the cranking amperage to start outboard engines. These are a versatile battery type and as long as the amp hour rating falls within the guidelines of the below chart these batteries are a great choice for powering trolling motors or other accessories.

Important note: is that when powering a 24 or 36-volt trolling motor system, it is not recommended to use a single battery in the 24 or 36-volt series as a starting battery as it can draw current unevenly from the system and over time lead to battery damage.

What is Marine Battery Group Size or GCI Group Size?

When shopping for trolling motor batteries you will find quite a few ways batteries are identified. One of those is called group size. Though there are a wide variety of sizes, the most common you will see are 24, 27, and 31 in marine applications. 

While this size nomenclature might be confusing at first, it’s merely a way to identify the actual physical size of the battery (Length x width x height) apart from its amperage or voltage rating. This is important for determining where batteries will fit in marine and automotive applications and is an industry-standard. The approximate size in inches for batteries in each of these group sizes is listed below:

 Amp Hour Rating

Ampere (Amp)-Hour rating is another consideration and method of comparing similar marine battery styles. It is the rating used to tell consumers how much amperage a battery can provide for exactly one hour. Said another way, the Amp-Hour rating is how long the battery will be able to maintain a charge while outputting a given amperage.

For a battery that has a 100 amp-hour rating, powering a trolling motor that is drawing 20 amps, the battery will last 5 hours if constantly running (100 amp hour battery / 20 amps drawn = 5 hours of run time).

A Minn Kota trolling motor will operate with any lead-acid, deep cycle marine 12-volt battery/batteries. For best results, use a deep cycle, marine battery with at least a 110-ampere hour rating, usually a Group 27 or higher. If amp hour rating is not available, select a deep cycle battery with a minimum of 180 minutes of reserve capacity.

Cranking Amp Rating

Another rating you might stumble across in search of the perfect battery is a cranking amp rating. Usually found on cranking/starting batteries for outboard engines and are less applicable to powering a trolling motor, because they focus on quick, strong burst of power to start your outboard engine vs long-lasting power for trolling motor use.

Cranking amps can usually be found rated as either CCA (Cold Cranking Amps) or MCA (Marine Cranking Amps). The rating outlines the number of amps a battery can deliver for 30 seconds while maintaining a voltage of at least 1.2 volts per cell – or 7.2 volts total for common six cell batteries. CCA is this measurement at 0° F and MCA is measured at 32° F to simulate a more realistic marine environment.

As previously noted, this is something you will need to check with your outboard manufacturer since cranking amps are a consideration more for starting batteries than for trolling motors.