What Size Battery For Trolling Motor?

trolling botor boat battery size

Owning a car is one thing, and owning a boat is another. While most people can afford to own a four-wheel automobile, not everyone is privileged to own a boat. There’s just a lot of advantages to having your own boat, even if it’s just a small one that you can use for fishing.

Imagine being able to head to the open waters by the end of the week just to relax and have a view of the sun setting to the west. How about a weekend with your friends or loved ones trolling for fish for dinner? There’s just nothing that will compare to a fresh catch!

But what if one day, you’re in the middle of the lake or the sea, and then suddenly your battery just dies?! That would be a nightmare!

It’s a good thing you can always plan by finding out what size battery for trolling motor. But before anything else, you must be aware of the types and usage of batteries for boats.

The Two Types of Motor Batteries

Most trolling boats are powered by 12-volt batteries. Now, there are two types of 12-volt batteries, the first one being for cranking, or starting, the main engine. This battery is designed to deliver short, yet high-current bursts required to get the job done.

The second type is the deep-cycle battery. This type is used for powering all your boat’s electrical accessories, including radios, fish-finders, and trolling motors. And then there’s the dual-purpose battery that’s designed to perform the functions of both the cranking battery and the deep-cycle battery.

Engine-Cranking Battery

As mentioned, engine-cranking batteries deliver high currents in short bursts. This means that this battery type has more surface area on the lead plates and can deliver more power. Engine-cranking batteries are designed to have thinner, yet more lead plates. They discharge only small portions of their capacity, with the energy quickly replenished as the engine runs.

Knowing the battery’s cranking, or starting, power is no rocket science, as the amp rating is indicated on the label. You can use any regular starter battery for almost all boat models, but if your ride features sophisticated digital parts and equipment, you would want to make sure that you don’t skimp on cranking power.

To find out how much power your boat’s motor needs, check the engine manual for the recommended marine cranking amp (MCA) rating before purchasing a battery. In the same manner, always select a battery with a rating that’s equal to the value recommended for your boat.

Deep-Cycle Battery

A deep-cycle battery is designed to be charged at the end of the day. Unlike the starter battery, it delivers charges to accessories, including the trolling motors, for long periods at a much slower rate. For this reason, deep-cycle batteries are made to have fewer, yet thicker plates. These thick plates are built to endure deep discharges.

If for a starter battery you’ll need to be aware of the cranking power, for a deep-cycle battery, what you need to be aware of is its reserve capacity (RC). Of course, starter batteries do have RC ratings, too, but for the function they have been designed for, their RC rating is not as much as important as it is for deep-cycle batteries.

The RC rating will let you know how long the battery can carry a determined load before discharging. Obviously enough, the higher the RC rating of the battery, the longer it will be able to power your boat’s accessories. Unlike a starting battery, a deep-cycle battery is designed to withstand numerous discharge and recharge cycles. It also typically has at least twice the reserve capacity of a starting battery.

Three Categories You Can Choose From

Batteries come in classifications, three of which are Wet-Cell, AGM, and Gel. Each has its pros and cons, and understanding how each type works will help you decide which one is best for your need.

Wet-Cell Batteries

Boaters are all familiar with traditional lead-acid, wet-cell batteries. These are also known as flooded-cell batteries, with each cell containing a liquid mixture of distilled water and sulfuric acid. What makes this battery the most favorable options among boaters is that it’s generally cheaper and carries a number of advantages.

For instance, when properly maintained, a high-quality wet-cell battery is able to endure over a thousand discharge and recharge cycles, which can translate to years of use.

These types of batteries are also less susceptible to overcharging. What’s more is that they tend to be lighter when compared to other battery types. The only drawback of wet-cell batteries is that they usually have vented designs, which means they need regular inspection. They also need to be maintained by topping them off with distilled water.

Moreover, this battery type is a bit fragile, and may not last long when exposed to constant high vibrations.

AGM Batteries

Another type of battery you can consider is the AGM. This battery type is designed with a filling of absorbent glass matting that’s tightly contained between the plates. The matting of an AGM battery is permeated by acid electrolytes. This means less maintenance, except of course for periodic cleaning of the battery’s exterior.

One major advantage of an AMG battery is that it’s tightly sealed, which means it has a lower risk of acid spillage. It also means it doesn’t release any form of gas at all. This battery type is also very versatile since it can be installed at any position.

And finally, since it’s highly resistant to shock and vibration, it’s the ideal battery to use under extreme conditions. The drawback? Due to the quality of its performance, it’s expected to be pricier than other battery types.

Gel Batteries

Gel batteries are similar to AGM batteries in a way that they utilize recombinant technology. This means they are maintenance-free. They are also sealed, with high tolerance to low-temperatures, and are resistant to shock and vibration.

Moreover, they have a very long life cycle. What makes Gel batteries special, though, is that they are highly resistant to over-discharging, one of the most common causes of damage in batteries. They have a self-discharge rate of less than one percent per month, which means you won’t have any problem at all storing them for extended periods without recharging.

This quality of Gel batteries makes them one of the ideal types of batteries for boaters who have a habit of forgetting to recharge their batteries right after use.

The downside of this battery type is its price since it’s generally more costly than other types of battery with the same MCA and RC ratings. They also need to be recharged correctly, or they’ll be at risk of suffering premature failure, something you wouldn’t want to happen right when you’re in the middle of the sea.

Picking the Right Type of Battery for Your Boat

When we say picking the right battery for your boat, we’re not just talking about picking the right brand or size. Both are important, but what’s more crucial is knowing which type of battery to select. One thing you must always keep in mind is that you can never substitute a starting battery for a deep-cycle battery, and vice versa.

If you use a deep-cycle battery as substitute for a starter battery, for instance, it won’t provide the needed power to crank up your outboard. On the other hand, if you use a starter battery in the stead of a deep-cycle battery, the battery will eventually fail, leaving your boat without power.

For that reason, it’s best to install one cranking battery and one deep-cycle battery for your boat. But what if your boat has a provision for only one battery? Well, if that’s the case, you will do best with a dual-purpose battery. A dual-purpose battery, as the name suggests, is designed to handle both starting and cycling.

Bear in mind, though, that a dual-purpose battery cannot provide the same power for the same purposes that an individual starter or deep-cycle battery is designed for. This means you can’t expect it to be as efficient as a starter battery in cranking up an engine or as enduring as deep-cycle batteries.

We have prepared an article about the best marine battery for your trolling motor!

The Perfect Battery Size for Trolling Motor

Now that you’re familiar with the different types of batteries you can choose from for your trolling motor, let’s move on and discuss battery size. The size of the battery you’ll need for your boat will depend directly on how big and heavy your boat is. When deciding on the battery size, we don’t decide on the physical size of the battery per se, but on the amount of power it can hold and deliver.

Trolling motors are rated by Newtons in the metric system, or by “pounds of thrust.” If you have a trolling motor with a capacity of 75 pounds of thrust, for instance, it could be comparable to 746W or 1hp. As a rule of thumb, for every 200 pounds of your boat’s gross weight, you will need 5 pounds of thrust.

Trolling motor batteries are usually available in 12-volt, 24-volt, and 36-volt capacities. A 12-volt motor is capable of consuming around 720W of power, so if your vessel is 16 feet in length or more, you might want to consider a 24-volt motor instead.

There you go. We hope this post was able to answer the question of what size battery do i need for my trolling motor you should choose for your boat. If there’s anything else you would like to know related to the subject, please don’t hesitate to share your thoughts in the comments section.

Find out more different type of battery you are interested in at Battery Man Guide!