Curious about the right battery size for your trolling motor? Navigating the waters of battery selection can be confusing, but worry not.
In this article, we’ll unravel the mystery and provide you with clear, actionable insights.
Get more power out of your trolling motor and enjoy your water adventures with less uncertainty.
What Is The Appropriate Size Battery For Trolling Motor?
For a trolling motor, it’s best to use a 12-volt deep cycle marine battery with a minimum 110 amp-hour rating. Higher amp-hour ratings provide longer run times, ensuring reliable power for your trolling motor.
Battery size chart for trolling motor:
| Trolling Motor Voltage | Battery Size | Number of Batteries |
|---|---|---|
| 12 volts | 12-volt | 1 |
| 24 volts | 12-volt | 2 |
| 36 volts | 12-volt | 3 |
Types of Trolling Motor Batteries
There are three main types of batteries that you can use for your trolling motor: lead-acid, AGM (absorbed glass mat), and lithium-ion.
Lead-Acid Batteries
Lead-acid batteries are the oldest and most common type of batteries for trolling motors.
They are made of lead plates submerged in acid (electrolyte) inside a plastic case. They are also the cheapest type of batteries, but they have some drawbacks.
They are heavy, bulky, prone to spillage, require regular maintenance (adding distilled water), and have a shorter lifespan than other types of batteries.
They also lose their charge faster when not in use and suffer from sulfation (buildup of lead sulfate crystals) that reduces their performance.
AGM (Absorbed Glass Mat) Batteries
AGM batteries are a newer and improved type of lead-acid batteries.
They have glass mats that absorb the acid inside a sealed case, which prevents spillage and reduces maintenance.
They are also more resistant to sulfation, vibration, and temperature changes than lead-acid batteries.
They are lighter and more compact than lead-acid batteries, but they are also more expensive.
They also have a lower self-discharge rate than lead-acid batteries, which means they can hold their charge longer when not in use.
Lithium-Ion Batteries
Lithium-ion batteries are the newest and most advanced type of batteries for trolling motors.
They are made of lithium cells that store and release energy in a chemical reaction.
They are the lightest and most compact type of batteries, but they are also the most expensive.
They have the highest amp-hour rating per weight and volume than any other type of battery, which means they can run your trolling motor longer and faster with less weight and space.
They also have a very low self-discharge rate and a longer lifespan than other types of batteries.
They require special chargers and protection circuits to prevent overcharging, overheating, or short-circuiting.
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Calculating the Right Battery Size
There are many factors that can affect your power consumption and run time, such as:
Amp-Hour Ratings
The amp-hour rating of a battery is the amount of current that it can deliver for one hour.
For example, a 100 amp-hour battery can deliver 100 amps for one hour, 50 amps for two hours, or 25 amps for four hours, and so on.
This rating is based on a constant discharge rate, which is not realistic in real-world scenarios.
When you use your trolling motor, you will vary your speed and direction, which will change the current draw.
Also, the amp-hour rating of a battery decreases as the discharge rate increases.
For example, a 100 amp-hour battery may only deliver 80 amp-hours at a high discharge rate.
Voltage Requirements
The voltage requirement of your trolling motor depends on the number of wires or terminals that it has.
Most trolling motors have either two wires (12 volts), three wires (24 volts), or four wires (36 volts).
The higher the voltage, the more power and speed you will get from your trolling motor.
You also need to match the voltage of your battery to the voltage of your trolling motor.
For example, if you have a 24-volt trolling motor, you need to connect two 12-volt batteries in series to get 24 volts.
If you have a 36-volt trolling motor, you need to connect three 12-volt batteries in series to get 36 volts.
You cannot use a single 12-volt battery for a 24-volt or 36-volt trolling motor, or vice versa.
In general, a 24-volt trolling motor requires at least two 12-volt batteries.
Estimating Power Consumption
The power consumption of your trolling motor depends on the thrust level that you use. Thrust is the force that pushes your boat forward, measured in pounds.
The higher the thrust, the more power and speed you will get from your trolling motor. You also need more battery power to sustain a higher thrust level.
Most trolling motors have a variable speed control that allows you to adjust the thrust level from zero to maximum.
The maximum thrust level is usually indicated on the label of your trolling motor, along with the maximum current draw at that level.
For example, if your trolling motor has a maximum thrust of 55 pounds and a maximum current draw of 50 amps, it means that it will consume 50 amps of power at full speed.
To estimate the power consumption of your trolling motor at different thrust levels, you can use this rule of thumb:
Power Consumption = Maximum Current Draw x Thrust Percentage
Thrust Percentage is the fraction of the maximum thrust that you use. For example, if you use half of the maximum thrust, the thrust percentage is 0.5.
If you use three-quarters of the maximum thrust, the thrust percentage is 0.75.
For example, if your trolling motor has a maximum current draw of 50 amps and you use half of the maximum thrust, you can calculate the power consumption as follows:
Power Consumption = 50 x 0.5 = 25 amps
This means that your trolling motor will consume 25 amps of power at half speed.
Considering Reserve Capacity
The reserve capacity of a battery is the amount of time that it can deliver a constant current of 25 amps before reaching a low voltage limit of 10.5 volts.
This is an indicator of how long your battery can last in case of an emergency or unexpected situation.
The higher the reserve capacity, the longer your battery can run without being recharged.
The reserve capacity of a battery is usually expressed in minutes and can be found on the label or specification sheet of your battery.
To estimate how long your battery can last at different power consumption levels, you can use this formula:
Run Time = Reserve Capacity x Battery Efficiency / Power Consumption
For example, if your battery has a reserve capacity of 180 minutes and an efficiency of 0.85, and your trolling motor consumes 25 amps of power at half speed, you can calculate the run time as follows:
Run Time = 180 x 0.85 / 25 = 6.12 hours
This means that your battery can run your trolling motor for about 6 hours at half speed before needing to be recharged.
Factoring in Safety Margins
The safety margin is the amount of extra battery capacity that you should have to avoid running out of power or damaging your battery.
It is recommended that you never discharge your battery below 50% of its full charge to prevent sulfation and reduce its cycle life.
This means that you should only use half of the available amp-hours in your battery for your trolling motor.
For example, if your battery has a capacity of 100 amp-hours, you should only use 50 amp-hours for your trolling motor.
You should also have some extra safety margin to account for the variations in power consumption, battery performance, and environmental conditions.
A good rule of thumb is to have at least 20% more battery capacity than what you need.
For example, if you need 50 amp-hours for your trolling motor, you should have a battery with at least 60 amp-hours of capacity.
To calculate the minimum battery size that you need for your trolling motor, you can use this formula:
Minimum Battery Size = (Trolling Motor Power x Usage Time) / (Battery Efficiency x Safety Factor)
Safety Factor is the fraction of the battery capacity that you want to use for your trolling motor.
For example, if you want to use 50% of the battery capacity and have a 20% safety margin, the safety factor is 0.5 x 1.2 = 0.6.
For example, if you have a 12-volt trolling motor that draws 40 amps of current, and you want to use it for 4 hours, you can calculate the minimum battery size as follows:
Minimum Battery Size = (12 x 40 x 4) / (0.85 x 0.6) = 376 amp-hours
This means that you need a 12-volt battery with at least 376 amp-hours of capacity to power your trolling motor for 4 hours with a 50% discharge limit and a 20% safety margin.
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Factors Affecting Battery Size Selection
Besides the voltage, amp-hour rating, and power consumption of your trolling motor, there are some other factors that can affect your battery size selection.
These include:
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Trolling Motor Thrust
The thrust of your trolling motor is the force that pushes your boat forward, measured in pounds.
The higher the thrust, the more power and speed you will get from your trolling motor. You also need more battery power to sustain a higher thrust level.
The thrust of your trolling motor depends on the size and weight of your boat, the wind and water conditions, and your personal preference.
Generally, you should have at least 2 pounds of thrust for every 100 pounds of boat weight.
For example, if your boat weighs 2000 pounds, you should have a trolling motor with at least 40 pounds of thrust.
Usage Duration
The usage duration is how long you plan to use your trolling motor in hours. The longer you use your trolling motor, the more battery power you will consume.
You should choose a battery with enough capacity to last for your desired usage duration.
You can estimate your usage duration by considering how often and how long you go fishing or boating, and how much time you spend using your trolling motor versus drifting or anchoring.
Boat Size and Weight
The size and weight of your boat can affect your battery size selection in two ways. They determine the thrust level that you need from your trolling motor.
As we mentioned earlier, larger and heavier boats require more thrust to move and steer them. They affect the space and load capacity that you have for your battery.
Larger and heavier boats usually have more room and can carry more weight than smaller and lighter boats.
They can accommodate bigger and heavier batteries without compromising their stability and performance.
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FAQs on What Size Battery For Trolling Motor
What type of marine battery is best for a trolling motor?
Use a deep cycle marine battery, not a starting battery. Deep cycles are designed to provide steady power over long periods.
How long will a marine battery run my trolling motor?
With periodic recharging, expect around 100 cycles from a quality deep cycle battery. Actual runtime depends on motor size and usage.
What size battery for a 30 lb thrust trolling motor?
A 30-55 amp hour deep cycle battery is commonly recommended for most 12V 30lb thrust trolling motors.
What about a bigger 55 lb thrust trolling motor?
For 55lb thrust, go with at least a 70-100 amp hour deep cycle to provide enough sustained power.
Is it better to use one battery or wire two together?
Start with one adequately sized battery. Wiring two together increases range but charges and discharges unevenly.
How can I get maximum battery life?
Completely Recharge After Each Use, Clean Terminals Regularly, Store Indoors, And Avoid Deeply Discharging.
Final Reflections
Selecting the appropriate battery size for your trolling motor is crucial for a smooth and enjoyable boating experience.
By considering voltage, amp-hour rating, and your specific needs, you can ensure a reliable and long-lasting power source.
So, equip your boat wisely and embark on your adventures with confidence.
