Trolling Motor Power Considerations

If your trolling motor is not getting enough power, it will not work properly. If you are having issues with your trolling motor, the first step in troubleshooting is to check the power to the motor. Batteries lose power over time if they have been sitting unused. As batteries age, they will have less life per charge. Overly deep discharges will cause sulfation that will reduce the batteries ability to provide power, damage from shock and vibration can destroy battery performance. even new batteries are prone to failure. It is always a good idea to check your batteries regardless of how old they are.

Calculating Runtime

The battery(s) for your trolling motor need to provide sufficient amperage and have a high enough amp hour rating to provide power for your motor usage. This link will take you to a downloadable PDF with the formulas for calculating Approximate Runtime, Approximate Speed in Miles per Hour and Approximate Horsepower. As a general rule, we recommend a 110 amp hour (Ah) rating per battery for 6-8 hours of runtime. If you have a lower Amp Hour rating, you will want to calculate the runtime for your motor. The chart below will show the max amp draw for your motor based on the thrust. If your battery(s) do not have a high enough Ah, you can connect additional batteries in parallel to increase the runtime. This link will walk you through creating parallel connections with additional batteries. When calculating runtime, we cannot determine amp draws at less than max amp draw as the boating conditions like boat weight, current, and wind will affect the actual amp draw.
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Selecting Battery Quantity

The number of batteries needed is determined by the trolling motor. If the motor is 55 lbs. of thrust or less, you will need (1) 12 volt battery. If you have a motor with more than 55 lbs of thrust up to 80 lbs. of thrust, you will need (2) 12 volt batteries for a total of 24 volts. If you have a motor with more than 80 lbs of thrust you will need (3) 12 volt batteries for a total of 36 volts. If you have an E-Drive motor, you will need (4) 12 volt batteries for a total of 48 volts. If you have a 24 volt, 36 volt, or 48 volt motor you will need to connect the batteries in series. This link will walk you through a series connection. The chart below will show how many batteries and the voltage needed by thrust.

Selecting Battery Group Size

The type of battery you choose will be affected by the features you want and available space in your boat. Larger group size batteries are larger in physical size and usually have a higher Ah rating.  The chart below shows average runtime based on the Amp hour rating of the battery and generally associated group size

Battery Types

Trolling motors can be used with Flooded Lead Acid batteries, AGM batteries, Gel batteries, and Lithium batteries. The different types of batteries have different features that may affect your battery choice.

  • Flooded Lead Acid
    Flooded Lead Acid, or FLA, batteries use a balance of water and battery acid to store the charge. If the balance of the fluids in the battery is off, the capability of the battery to charge, hold a charge, and dispense the power will be affected. Flooded Lead Acid batteries are in general cheaper than other types of batteries but require more maintenance than other types. They need to have the fluids checked and topped off on occasion. Your battery manufacturer can help you with maintenance specific to your battery. As an FLA battery is discharged, the level of power the battery can provide tapers off.
  • AGM
    AGM or Absorbent Glass Mat batteries are sealed batteries that use Flooded Lead Acid technology without the maintenance. They are more expensive than FLA batteries but require less time to take care of. Just like with an FLA battery, the level of power an AGM battery can provide tapers off.
  • Gel
    Gel batteries are sealed batteries that use silica or sand to convert the battery acid into a thick gel. Gel batteries are maintenance-free and spill-proof because of the gel, but they are also sensitive to temperature. The gel can be burned if the battery is used in a high-amp situation. They are also more expensive than FLA batteries but require less time to take care of and are spill-proof. Just like with an FLA and AGM battery, the level of power a Gel battery can provide tapers off. Gel batteries also require special charging considerations.
  • Lithium
    Lithium batteries are the most expensive batteries when compared to FLA or AGM batteries. They do not need the level of maintenance FLA batteries require. Lithium batteries provide consistent power until the battery is dead. The power provided by the battery does not taper off like FLA or AGM batteries do. Lithium batteries will have more specific requirements for charging. The battery manufacturer can tell you what is needed for charging.
    • Continuous Discharge Amperage
      When using lithium batteries, you want to ensure the battery(s) provide(s) enough continuous discharge amperage to run the motor at its max amp draw. The chart below shows the max amp draw by motor thrust. If the motor is not getting enough amperage, it will have issues including working for a short time and then shutting off, being able to turn on the motor but not turn on the prop, steering issues, issues with i-Pilot and i-Pilot Link such as Spot Lock not working or being erratic. If you are having any issues with your motor and you are using Lithium batteries, verify you have enough continuous amperage available for the motor to pull its max amp draw.
    • Power Output
      Lithium Batteries maintain higher voltages for longer. Motors engineered to make the most of flooded lead acid batteries can be damaged by the higher power output. To prevent this damage when using Lithium batteries you should not run your motor at its highest speeds, staying at 85%/Speed 8.5 or lower.

Checking Power

After verifying your batteries are capable of providing proper power to your motor, you will need to follow the steps below. These steps are important to determine if you have an issue with your power, what that issue is and where it is located. If you find an issue with your power, you will need to resolve it for proper operation of your trolling motor.

  • Load Testing
    As a battery discharges the voltage of the battery decreases. While batteries can typically be recharged from very low voltages you should consult your battery manufacturer regarding what voltage level the battery experiences damage that will limit its capacity in the future. Motor performance is highly dependent on consistent voltage, the battery system (battery and wires) should not experience more than 5% drop. To verify the battery system is good you can monitor the voltage as close to the motor as possible, when the motor is running on high, in the water, the voltage must not drop more than 5% (0.6 V on a 12 Volt system, 1.2 V on a 24 Volt system, 1.8 V on a 36 Volt system). If this is not practical the batteries can be individually tested using a load tester, then verify the wires are the correct gauge as identified on the Minn Kota wiring chart, and all the connections are clean (free of corrosion) and mechanically tight.
  • Verifying Power
    You can check your power by using a voltmeter to test the voltage coming off of your battery(s) and then comparing it to the voltage at the Quick Disconnect or Plug and Receptacle if you are using one and then again at the motor. The voltage at the Quick Disconnect/Plug and Receptacle and at the motor should match the voltage from the battery(s). If it does not, you are dropping power between the battery(s) and Quick Disconnect/Plug and Receptacle or Quick Disconnect/Plug and Receptacle and the motor or if you are not using a Quick Disconnect/Plug and Receptacle, between the battery(s) and the motor.
  • Connections
    If you are having issues with your motor and the batteries are charged, have been load tested (FLA, AGM or Gel) and are testing good, you will want to check the connections between the trolling motor and battery(s). The connections should be clean and tight. If there is any corrosion, buildup, or anything contaminating the terminals or connectors, they should be cleaned and then reconnect the terminals or connectors.
  • Quick Disconnects and Plug and Receptacles
    If you are using a Quick Disconnect or Plug and Receptacle, check the connections coming from the motor into the quick disconnect or the plug to verify the connections are secure and the polarity is correct. Also verify the connections are clean with no buildup and no damage to connectors. Damage, corrosion, buildup, and loose connections can cause issues with power transfer. Next check the connections coming from the battery(s) to the quick disconnect or receptacle. Again you want a clean and tight connection with no buildup and no damage to prevent power transfer.
  • Circuit Breaker
    The circuit breaker should be appropriate to the trolling motor. The chart below will show what circuit breaker is needed by motor. Verify the circuit has not been tripped and is in good condition. Also verify the circuit breaker connections are clean and tight and there is no buildup on the terminals.
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  • Wiring and Wire Size
    The wiring from the motor to the batteries should be of a suitable gauge and in good condition. If you have wear on the lines or there is a break in the lines, you will have issues with power reaching the motor and could have a fire onboard. The chart below will assist in determining what gauge wire you need for the motor and the distance between the battery leads coming off of the motor and the batteries.

    Visually inspect your wires looking for any wear marks, kinks, or cuts. If you see any, replace the wires with appropriately sized wires from the chart below. You can check for breaks in the lines by testing each line for continuity with a continuity tester. Another method, although not as reliable, is to feel the lines while they are in use, any warm spots indicate an issue.
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