Calculating Amps Per Hour

Calculating trolling motor battery
Calculating trolling motor battery

You might be wondering just how long your motor will last. This is a common concern, but unless you know what to look for, you might not be able to find out if the battery you have is built to last. When it comes to accurately figuring out whether your battery will last or not, you’ll have to first figure out the battery’s amperage hour rating, and also your trolling motor’s amperage draw number. So if you can figure out just how long your trolling motor will last and figure out these two values that we’ve spoken about, you’ll be able to get the right trolling motor battery for the job and get that much closer to getting your boat ready to go out on the water. So in this post we’re going to go into things like amperage hour rating and motor amperage draw in order to get a better understanding for how these things work. First let’s start by understanding what we mean when we say amperage hour rating.

Amperage Hour Rating

The way that amperage hours work is basically that they show you just how long the battery can supply the trolling motor with power. In order to break it down into more simple terms, a battery that has a 100 amperage hour rating can actually give your trolling motor 25 amps of power for a total of four hours. If instead you wanted to use this particular battery for ten hours, you could use it at 10 amps before it’ll lose a charge, useful for those longer trips you might want to go on. In either case, what you want to do to calculate the amps per hour is basically to take the amps that you’re looking at using and then multiply that number directly with the amount of hours that the battery will be running for. And so, now that we’ve gotten a handle on what goes into forming the amperage hour rating, let’s take a look at what makes up the motor amperage draw.

Motor Amperage Draw

When it comes to figuring out the estimated run time of your trolling motor, along with the amperage hour rating you’re going to need to figure out what your motor amperage draw is. What the motor amperage draw rating is is basically the amount of amperage (also known as current) that a motor is going to pull in at whatever speed the motor might be operating at. While your particular motor’s amperage draw number might not be exactly easy to find, you can always figure it out by consulting with the motor’s original manufacturer, or you can count on resources like Basically, you’ll need to take the amperage hour rating of your battery and then divide what you get by the amperage draw. Now that we’ve gotten a good handle on what goes into the amperage hour rating and motor amperage draw, let’s take a look at some of the ways that you can maximize the way that your motor runs.

Be sure to consider weather conditions.

Weather as well as water conditions can severely impact the way that your motor and its battery are going to run once you take your boat out on the water. For example, a motor that usually takes 20 amps to run might suddenly require 30 amps to move that boat if you’re facing some seriously choppy conditions. So if you’re the type who likes to challenge Mother Nature, be sure to take this into account before going into the water. But aside from weather considerations, you’re going to want to keep the following tips in mind when it comes to extending your motor’s battery life.

Extending Battery Life

One of the ways you can make sure that your battery lasts as long as possible is to use a variable speed motor. This will allow you to be much more energy efficient, especially if you’re planning on running at a slower speed. There’s also more room to customize, as you can dial in to the exact speed that you want instead of having to select from a pre-determined speed that might not suit your needs. Along with this, buying a large motor will help to extend your boat’s battery life, and another thing to think about is not fully depleting your battery, as doing so is going to greatly reduce your battery’s overall lifespan.

Go ahead and get out on the water!

So as you can see, by figuring out your amperage hour rating and motor amperage draw, you’ll be able to maximize your battery’s overall lifespan and stay out on the water for longer. So now you can get back out onto the water instead of worrying about your boat’s motor.