Determining the appropriate size for your trolling motor battery depends on several factors, such as your usage, available space, and boat weight. Large capacity is great, but it should be small enough to fit your boat size. So, what’s the correct battery size for you?
An electric trolling motor needs a Group 27 size battery for standard use. Ideally, it should be a 12-volt, deep cycle, marine battery with an amp hour rating of 110 or above. However, not all batteries have an amp hour rating, so get one that provides at least 180 minutes of reserve capacity.
Besides the size, you should also make sure you get the right battery type for an electric trolling motor. It should be big enough to be reliable, and it should be the right type for maximum efficiency and lifespan. This article will help you get it right — let’s begin!
Choosing the Right Battery Size for Electric Trolling Motor
Finding the optimal battery size for your electric trolling motor requires considering several factors. The amount of thrust, amperage, reserve capacity, or voltage you need has a lot to do with factors like your boat weight, length, and usage.
You’ll also need to look into what type of battery would be best. They include:
- Lead Acid Wet-Cell batteries are the most popular and should last a few years.
- AGM (Absorbed Glass Mat) batteries can cost twice as much as lead acid wet-cells, but they can last twice as long.
- Lithium batteries are not as popular but are lightweight and can last as long as ten years.
As mentioned, the common choice would be a Group 27 rated battery with a minimum of 175-180 minute reserve or at least 100 amp hours. That said, if you want to spend more, you could go for a Group 31 battery.
A 24-volt battery is typically comprised of two identical 12 volt batteries with the same amp hour or reserve minute rating as above. Likewise, you will need 3 12 volt batteries for a 36 volt electric trolling motor following the same rule.
Let’s take a closer look at some of the factors you should consider before purchasing a battery for your electric trolling motor.
Check out our Review of the Top Electric Trolling Motor Batteries
Heavier Boats Need More Thrust
A battery’s size relates to the amount of energy it can carry and deliver, which also is a factor for how much thrust it can offer. Hence, the boat weight is crucial for determining the appropriate battery size for your electric trolling motor.
The heavier your boat is, the more thrust it needs to move around. As a general rule of thumb, you need 2 pounds (0.90 kg) of thrust for every 100 pounds (45.35 kg) of boat weight.
For instance, if you’ve got a boat that weighs 4000 pounds (1814.36 kg), it’ll need about 80 pounds (36.28 kg) of thrust.
The Formula for Calculating Required Thrust
Divide the highest potential boat weight by 100 and multiply it by 2 to determine how much thrust you need in pounds.
For example: 4,000 lbs ÷ 100 × 2 = 80 lbs
Tip: Make sure you consider the highest potential boat weight for battery size calculation. This means adding up the weight of your boat, your fishing gear, the maximum number of passengers, and even the batteries! Of course, you can also add a few more pounds just in case.
Finding Out Boat Weight
The easiest way to find out your boat weight is to visit your boat manufactures website or a boat directory and look up your make and model. These directories have thousands of boat models organized by model, manufacturer, weight, and length.
Remember that the listed weights you’ll find will be of the boat alone. Don’t forget to follow the above tip to get to the maximum potential boat weight for thrust calculation.
Note: pontoon boats will require a bit more thrust to maneuver as they tend to hold a very straight line.
The Battery Needs To Fit Along With Supplies and Equipment
The higher your battery’s reserve capacity, the safer you’ll feel in any scenario. Similarly, you’d also prefer having more thrust to power your boat.
However, one of the most significant limitations that get in the way of having bigger trolling motor batteries is the available space on your boat. Of course, you’d love a super strong battery that lasts long, but can you even fit it in your boat?
As discussed above, your thrust requirements vary with your boat’s weight and size. Therefore, you should find a battery (or a set of batteries) that provides sufficient thrust without being too big to fit onboard.
You should also consider the weight of your batteries, as too much of it might not be ideal for your boat’s balance.
Make sure to account for the amount of space you need for yourself and all your fishing gear aside from the batteries.
Heavy Boat Usage Often Requires Bigger Batteries
The right battery size for an electric trolling motor also depends on how you plan on using the boat. Ask yourself the following questions:
- Are you moving around a lake?
- Are the conditions windy?
- Will there be a strong current in the river?
Depending on the conditions, you might need larger batteries to deal with challenging usage.
Thrust Requirements in Rough Conditions
As fishing conditions get rougher, the boat might require more thrust for a smoother fishing experience. That’s especially true if you’re planning on spending most of your time in strong waves, currents, or fast-moving water.
You should ideally be able to stick to the minimum thrust levels in any condition; however, you might require to go above and beyond the recommended thrust levels to ensure sufficient power delivery in any fishing scenario.
Starter Battery vs. Deep Cycle Battery
We’ve discussed the factors determining the correct battery size for your electric trolling motor, but not all batteries are alike.
Different types of batteries power boats — some are only meant to power the ignition to start the boat’s engine (starter batteries). In contrast, other batteries provide constant power for boat functions (deep cycle batteries).
Some batteries can also take care of both of these uses, i.e., ignition and power delivery — they’re known as dual-purpose batteries.
Let’s look at both these types.
Starter Battery
Starter batteries are meant to crank the engine. Being ignition batteries, they’re designed to provide a strong current in short bursts to start the boat’s engine. Then, like in a vehicle, the starter battery recharges as the boat runs.
These batteries are inherently different from deep cycle batteries since they fulfill a unique purpose. The biggest difference in starter batteries is having a greater number of lead plates with a large surface area.
I’d suggest looking at your boat motor’s owner’s manual to check the recommended battery specification required to start the boat. It should be identified as the marine cranking AMP (MCA).
Most traditional boats can start using any starter battery, but it’s better to handle some of them according to the recommended battery specifications for increased lifespan and efficiency.
Note: There is a difference between Marine Cranking Amps (MCA) and Cold Cranking Amps (CCA). Each is a rated number of amps the battery can deliver for 30 seconds. Cold Cranking Amps (CCA) is rated at 0 degrees F, and Marine Cranking Amps (MCA) is rated at 32 degrees F.
Here is a conversion:
CCA x 1.3 = MCA
MCA x 0.77 = CCA
Deep Cycle Battery
An electric trolling motor will also need a deep cycle battery to power the boat. This type of battery is intended to be cycled or discharged to 50% many times.
Unlike starter batteries, their power delivery comes at a slower rate. This is because they’re designed to be more sustainable for extended usage periods. Therefore, deep cycle batteries have fewer lead plates than cranking batteries.
One of the essential features of a deep cycle battery is its reserve capacity. It represents how many minutes the battery can deliver 25 amps before the battery reaches 10.5 volts. The higher its reserve capacity rating, the longer it’ll last at powering your electric trolling motor.
Amp-hours is a common measurement for most electric trolling motor batteries. This represents the battery’s total available amps it can deliver equally in 20 hours until it reaches 10.5 volts. A 100 amp hour battery should provide 5 amps per hour for 20 hours.
If your battery is only marked in a reserve capacity, try dividing the capacity by 2 and adding 10% to get an estimate of amp hours.
Example: RC / 2 x 1.1 = AH
Deep cycle batteries a meant to be used in applications like an electric trolling motor, RV, or solar system. The life span can be directly linked to how many times you discharge the battery to 50% depth of discharge. Time can affect your battery’s life span, but cycles are more significant.
| Battery type | Cycles (at 50% dod) |
| Wet-cell | 150-200 |
| AGM | 300-500 |
| Lithium | 3000-5000 |
Of course, the quality of the battery and maintenance make a difference, check with the manufacturer.
Helpful Battery Tips for Electric Trolling Motor Usage
Here are a few battery tips to keep in mind for efficient usage in electric trolling motors and a prolonged lifespan:
- Never mix different battery types for the same purpose (like using a deep cycle and cranking batteries for power delivery).
- Never mix old batteries with new ones.
- Keep a regular check on the fluid levels of a wet-cell battery and keep them filled to the recommended levels at all times.
- Try maintaining a trickle charge in the off-season and store them in a cool, dry place.
- Recharge the batteries after every trip as soon as possible as leaving batteries drained for an extended period can negatively impact their performance and health.
- Keep terminal connectors corrosion-free by periodically cleaning them with a mixture of water and baking soda.
Conclusion
If you’re in the market for the best battery to use with an electric trolling motor, you should stick to the recommended battery types and capacity levels in your owner’s manual. You need to get right two primary things — the battery type and the reserve capacity rating or amp hour rating.
You need a deep-cycle marine battery with sufficient power to provide the thrust for your boat’s maximum weight.
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