Do Trolling Motors in Boats Require Two Batteries?

May 9, 2024 2:12 pm Published by Leave your thoughts

Boating and fishing enthusiasts often find themselves pondering the necessity of multiple batteries for their equipment. A common query revolves around whether a trolling motor requires its own dedicated battery, or if a single battery can manage both the trolling motor and the boat’s starting engine. This blog will delve into this question, providing a comprehensive understanding of why having separate batteries might be beneficial for your boating needs.

The Role of Batteries in a Boat

Boats generally require batteries for two primary functions: starting the engine and powering auxiliary equipment, such as a trolling motor. These two functions demand different battery characteristics. Here is a detailed explanation of the requirements and differences between these batteries:

Starting Battery

The starting battery, as the name suggests, is designed to start the boat’s engine. It provides a short, high burst of power necessary to crank the engine and get it running. This type of battery is optimized for maximum current output in a short period, typically achieved through thin battery plates that offer a large surface area.

Deep Cycle Battery

In contrast, a deep cycle battery is designed to provide a steady amount of current over an extended period. This makes it ideal for applications like running a trolling motor, which requires sustained power for hours. Deep cycle batteries feature thicker plates, which can endure repeated discharging and recharging cycles without significant degradation.

Dual Purpose Battery

There are also dual-purpose batteries that aim to combine the features of both starting and deep cycle batteries. These have plate thickness that is intermediate between starting and deep cycle batteries, attempting to balance the demands of both starting the engine and powering auxiliary equipment. However, they often do not perform as well as dedicated batteries for either specific task.

Why Two Batteries?

A common question among boaters is:

I have a fishing boat with a trolling motor. I have been told I need two batteries? Why?

The reason is because the trolling motor operates differently than a starting battery for the boat motor. Sometimes a “dual purpose “ battery can do both jobs but you might not want this type of battery to do both jobs. If you use the same battery for starting and trolling motor, you risk discharging the battery too far so the boat motor will not start. The difference between each battery is the internal parts are different to better do each type of job.

A battery for starting has thin battery plates because the more plate surface area the more starting power. A battery for a trolling motor (deep cycle) has thicker plates to better withstand lower voltages over longer periods of time and still be recharged. A dual purpose battery has plate thickness between the starting battery and the deep cycle to try to accomplish both types of uses.

Detailed Analysis of the Need for Two Batteries

Risk of Discharging Too Far

One of the primary risks of using a single battery for both starting the engine and running a trolling motor is the potential for discharging the battery too far. Trolling motors can draw substantial power over long periods, which can significantly deplete the battery. If the battery is too depleted, it might not have enough power left to start the boat’s engine, leaving you stranded.

Different Charging Requirements

Starting batteries and deep cycle batteries also have different charging requirements. Using a single charger designed for starting batteries might not adequately recharge a deep cycle battery and vice versa. By using two separate batteries, each can be paired with the appropriate charger, ensuring optimal performance and longevity.

Longevity and Reliability

Using the appropriate battery for each function also contributes to the overall longevity and reliability of your boat’s electrical system. Starting batteries are not designed to be deeply discharged regularly, and doing so can significantly shorten their lifespan. Similarly, deep cycle batteries are not optimized for the high current bursts required to start an engine. Dedicated batteries for each function ensure that both starting and trolling are reliable and efficient, reducing the risk of battery failure when you need it most.

Practical Considerations

Space and Weight

While having two batteries can provide significant advantages in terms of reliability and performance, it also means additional weight and space requirements. Boats have limited storage, and finding a suitable place to install an extra battery can be challenging. Additionally, the extra weight can affect the boat’s performance and fuel efficiency. However, these considerations are often outweighed by the benefits of having a reliable and properly functioning electrical system.


There is also an additional cost associated with purchasing and maintaining two batteries instead of one. However, the potential cost savings from avoiding battery-related issues, such as being stranded with a dead battery or having to replace batteries more frequently due to improper use, often justify the initial investment.


While it is possible to use a single dual-purpose battery for both starting your boat’s engine and powering the trolling motor, this approach comes with significant risks and potential drawbacks. A dedicated starting battery and a separate deep cycle battery for the trolling motor provide a more reliable and efficient solution. This setup ensures that each battery is used in a manner consistent with its design, enhancing the overall longevity and performance of your boat’s electrical system.

By understanding the distinct requirements of starting and deep cycle batteries, boaters can make informed decisions that enhance their boating experience, ensuring they have the power they need, when they need it, without compromising the functionality of their vessel.

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