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Sunday 16 May 2021
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???? Batteries and Electronics ????

So you have a kayak and you like to fish, and now you’ve decided to install a fish finder. So after picking out that cool new unit you’ve been wanting, you realize that you need to get a battery and you’re wondering what size and type to purchase. Maybe you have a basic understanding of electrical principles, or maybe you have no idea what any of those numbers mean. This article is aimed at giving you a basic understanding of what you should know.

Basic Electrical Terms
There are some basic electrical terms you will need to understand. We’ll start off with voltage; in layman’s terms think of voltage as the force behind electricity. The more voltage you have, the more power you have available: you can equate this to water pressure. For this article we will limit ourselves to talking about 12VDC (Volts Direct Current), since that is what most fishfinders are designed to run on. However, most units are able to accept a range of voltages as wide as 10VDC to 20VDC without damage. We also won’t get into the difference between DC (Direct Current) (what powers your car) and AC (Alternating Current) (what powers your house) in this article, but please understand they are different and AC current is much more dangerous. The next terms you need to know are Amperes (A) (“Amps” for short) and milli-Amps (mA) (1/1000 of an Amp). Amperes is the measurement of the current or flow of electricity. In a water system you could equate Amps to GPM (Gallons per Minute). The last term you need to know is what an Amp/hour rating is. This is how a battery’s size is rated – the capacity of a battery. For example a 5 Amp/Hour battery will produce 1 A worth of power for 5 hours, like a 5 gallon bucket will produce 1 GPM for 5 minutes.

To figure out what size of battery you need, you have to first figure out how much power your fishfinder will use. This is one place where bigger is not necessarily better. As you can imagine, the more bells and whistles you have on your fishfinder the more power it will use. So that color, wide screen, HD, Down Imaging, GPS, sonar unit will use a lot more power than the small, black and white, sonar-only unit. The good news is most electronics companies will tell you what the mA draw of their units are. This is normally listed in the specifications section either on the website or in the owner’s manual. If you can’t find it, don’t be afraid to call the Tech Support line – they should be happy to help you out.

For this example we will use the Humminbird “598ci HD SI Combo” unit, which is rated at 615 mA with the lights off. Also please note this is normally a peak current rating, and your actual current draw may be less. If you have an appropriately-sized mA meter and know how to use it, you can place it in line and measure the actual current draw. When I measured my unit with the back light fully on, my peak measured current draw was 430 mA – over 25% less power than the rated draw with the light off. For calculation purposes, though, we will use the 615mA to add a safety factor, since most batteries will not match their rated performance more than a few times.
Now that we have an idea of how much power we will be using, we need to figure out how big a “bucket” we need. Since I regularly do long and multi-day fishing trips, I will use 12 hours for the minimum time I want my battery to last. If I take 12 hours X 615 mA = 7380 mAmp/hours. Divide that by 1000, and you get a 7.38 Amp/hour battery.