Can A Cranking Battery Be Used For A Trolling Motor? (3 Things You Need To Know)

UPDATED 31 JULY 2022

by Eric Bartlett

Batteries are essential for running your trolling motor, starting your boat engine, as well as running any other boat electronics that you may have.

But if you’re just getting started in the world of boating, it can be a little challenging to get the right batteries for all the different tasks on your boat, making it tempting to simplify matters by using one battery for all of your purposes.

So, can you use a cranking battery to run a trolling motor? In this article we’ll give you a detailed answer to this question, as well as walking you through the battery options available to you for running your trolling motor.

Can you use a starting battery for a trolling motor?

If you’re in a tight spot and don’t have another choice, then yes, a starting battery can be used for a trolling motor. However, this is not a good idea for regular use, since a cranking battery is not built for this job.

Not only does a starting battery perform poorly when used to power a trolling motor (in terms of a shorter run time compared to a deep cycle battery), but the deep discharge that results from this kind of use will damage the cranking battery, reducing its lifespan significantly if used repeatedly in this manner.

What is the difference between a starting battery and a deep cycle battery?

A starting battery is designed to deliver a short burst of high amp electricity to start the ignition of a combustion engine, followed by immediately being recharged by the alternator of the engine, once it has sprung to life.

A deep cycle battery, on the other hand, is built to deliver a long, steady current of low amp electricity intended to power an electric motor over many hours, and then to be slowly recharged by a charger specifically designed for this task.

If you’re currently in the market for a new trolling motor battery, check out our article: the least expensive lithium marine batteries reviewed.

Deep vs shallow discharge

Another key difference between the two types of batteries is that a cranking battery doesn’t tolerate a deep discharge very well, and will incur damage if repeatedly exposed to a deep discharge. 

Deep cycle batteries, on the other hand, are well suited for a deep discharge, and don’t get damaged from this kind of use.

In fact, when you purchase a new deep cycle battery, it’s advisable to discharge it as deeply as possible during the first several rounds of use, as that helps to increase its maximum runtime.

Also of note in this context is that lithium deep cycle batteries are able to provide a steady level of current no matter how deep their level of discharge, which means you can use them to run your trolling motor or other boat electronics at full power all the way until they are 100% discharged. 

In terms of physical differences, starting batteries are built with a large number of thin plates to maximize their surface area, thus allowing them to generate a stronger current.

In contrast, deep cycle batteries are designed with fewer and thicker plates, which reduces the surface area of the plates. This design provides less surface for electrolytes to react with, resulting in a slower current release.

Do you need a separate battery for a trolling motor?

Yes, it’s highly advantageous to have a separate battery for a trolling motor.

That way you can use a deep cycle battery for the trolling motor, and a cranking battery to start the boat engine, without having to abuse either battery by using it for incorrect applications.

This not only allows you to extend your battery lifespan, but also results in much better battery performance for each application.

The main exception to this is if you have a very small boat, such as a mini bass boat, and space is a limiting factor making it difficult to stow more than one battery on your boat. If that’s the case, you can opt for a dual purpose battery, and use just one model to cover all of your needs (more on that below).

Can you use a dual purpose battery for a trolling motor?

Yes, a dual purpose battery can be used to run a trolling motor, as well as doubling as a starting battery for your boat engine.

A dual purpose battery has a hybrid design that enables it to provide enough power to start the ignition of your boat engine, while also being able to provide a slow steady current over a long period of time to power a trolling motor.

In addition to this, a dual purpose battery can tolerate a deep discharge relatively well, so you don’t have to worry about damaging it when you use it for your trolling motor.

However, the downside of a dual purpose battery is that it isn’t as quite as good as either a cranking battery or a deep cycle battery. That means it won’t perform as well as one of these specialised battery types for any of the tasks you use it for. In addition to this, it won’t tolerate as many deep discharge cycles as a true deep cycle battery.

Because of this it’s usually best to install separate cranking and deep cycle batteries on your boat, but it may be better to use a dual purpose battery if your boat is too small to accommodate several batteries, and you need to conserve space by using a single battery.

Dual purpose battery vs deep cycle battery

A deep cycle battery tolerates discharge below 50% better than a dual purpose battery, and also withstands more charging cycles without any issues.

So if you want to use a dual purpose battery instead of a deep cycle battery, it’s best to avoid discharging it below 50% in order to extend its lifespan.

Dual purpose battery vs starting battery

A dual purpose battery withstands deep discharge much better than a starting battery. This is advantageous if you want to use your starting battery to power a trolling motor, or other electronic devices, such as lights, or a livewell, etc.

In a case like that it’s advisable to replace the starting battery with a dual purpose battery. Just keep in mind not to deplete the battery more than 50% in order to avoid reducing its lifespan too drastically.