How to Connect Fish Finder to Trolling Motor Battery

By Wade Johnson

How to Connect Fish Finder to Trolling Motor BatteryYou might find a few things complicated while searching for a fish finder. The existence of different brands in the market would prompt you to go for the right one, one that is less expensive, user-friendly and comes with advanced features. After you are done with selecting a good fishfinder, that is, one that provides ease with accurate data, you would need to install it.

This is where things get a bit hard. Well, with no previous knowledge of wiring a fish finder to a battery, the installation of a high-technology device that reads sonar data can possibly turn out to be quite a complicated job. When it comes to installing a fish finder, the first thing that makes sense to bother is the battery.

While installing a fish finder, there are two options that some anglers struggle with. First whether to connect a fish finder to a new battery or to a trolling motor battery. In this article, you would learn how a fish finder can be connected to a trolling motor battery.

Is it important to have a separate battery for a fish finder?

Well, the first question that makes more sense to have in mind is whether it’s good to have a separate battery for my fish finder or one battery is enough to do the job. Well, a dedicated battery helps to eliminate voltage drop issues from the trolling motor, and stator fluctuations as well. Plus, the ignition noise from the motor is also reduced. Both are considered very good things to eliminate, but in reality, the starting battery is usually good enough.

Is it really possible to connect fish finder to trolling motor battery

Lead-acid batteries are considered the most common deep cycle batteries for trolling motors. The best thing is that they can easily handle frequent draining. Re-charging is associated with trolling motor use and they are surely the most affordable option. If the quality of the battery is good, lead-acid batteries last between 2-3 years.

So, in order to connect a fish finder to a trolling motor battery, You need to connect a light gauge wire (usually 18 gauge is preferred) from the negative post of the trolling motor battery straight to the negative post of the engine’s cranking battery. If there is still some sort of interference,  just check the routing of the depth finder and trolling motor battery leads.

As a matter of fact, most recommend wiring your fish finder to the starting battery. If you connect your fish finder to the trolling motor battery, make sure that you keep in mind the effect of interference from having your fishfinder wired to the trolling motor batteries. You will get on-screen interference and you might run your trolling batteries down with electronics.

How powerful is a trolling motor battery?

Most of the trolling motor batteries are typically between 35 and 125 amp-hours. Plus, a more important number that experts advise to look at when selecting a trolling motor is the reserve capacity. Why? because the reserve capacity evaluates how long the battery will last with a 25 amp discharge.

Why is it better to have a separate battery?

According to many fish finder experts, while connecting your fishfinder to power, it is always recommended to use separate batteries for the fish finder and engine generator. Well, the possible logical reason for this is that there can be a lot of noise from the engine interfering with the signal to the fish finder. So in order to eliminate unnecessary noise and interference, it is suggested to install the power cable and transducer cable to the fish finder separately.

Things to consider while choosing a fishfinder battery

Weight and Size

The weight and size of a fish finder battery are of quite significance if you are using it on a kayak where every ounce is added up to the weight. Lithium-ion batteries are considered the lightest weight option, but they also come with a big price tag.

Battery power

All of the that comes around 12v batteries are rated for 10Ah (amp hours). It gives a level playing ground and its facilities with a great capacity for a full day of fishing running a fish finder sonar and possibly more electronics.

Battery construction

Usually, there are two major types of batteries that are considered suitable for use in a marine environment for powering fish finders. So, other types of batteries also exist but due to some environmental issues with them like not being properly sealed or inability to handle harsh environments they are not the best choice.


Although you can use a motor trolling battery to connect a fish finder, this is not considered a good practice. Instead of using a trolling motor battery, it is considered safe, efficient, and reliable to use a starting battery.

Wade Johnson
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