Eliminate The AA Batteries From Your Smartcast RF15

Everyone who owns a Humminbird Smartcast RF15 knows that it's invaluable for finding fish and analyzing the water temperature, depth and bottom structure in hard-to-get-too areas.

But even with all it's cool features which rival many of the higher priced boat mounted fish finders, the Smartcast RF15 has one little design flaw that tends to give it a bad name among fishermen who have used it.

The 8 AA Alkaline batteries providing power to the main fish finder don't last very long. After two or three hours the batteries start to get weak and significantly decrease the fish finders sensitivity and accuracy. And if you make the mistake of using old or generic batteries, the RF15 may not work properly from the first time you turn it on.

Misinterpretation of this problem and it's symptoms cause many RF15 users to get frustrated and they end up either putting their unit on a shelf somewhere to collect dust, or they end up selling it on Craigslist or eBay.

Below is a inexpensive and easy modification that will allow you to use your Humminbird Smartcast RF15 for several hours on just one battery charge. I have personally tested this power modification using the small 12vdc lead-acid battery depicted below for over 15 hours straight and the RF15 still kept working without fail.

If you plan to fish from shore, you probably aren't going to have access to a full-size deep-cycle marine battery like you would fishing from a boat, so you will need to get this small 12vdc lead-acid battery shown on the left.

This battery is small, inexpensive and because it's intended to be used in battery backup systems for computers, it will provide the steady and clean flow of electricity your sensitive electronic Smartcast RF15 demands.

This battery is about 7" wide x 4" tall x 3" deep and only weighs about 3 pounds making it the perfect companion for your Humminbird Smartcast RF15. It will power your fish finder for up to 20 hours of continuous use before it needs recharged.

Now we need a power cord that we can use to connect our new battery to the plug on the back of the Smartcast RF15.

This Platinum Series 12v cigarette lighter adapter extension is perfect for the modification we need. It's 10' coiled cord will allow us to strech it out about 6' from the RF15, but won't leave a bunch of excess cord to trip on when the battery is kept close to the fish finder.

Modify this 12v extension and adapt it to the battery and the Smartcast RF15 power cord following the instructions below.

Warning: Failure to follow these instructions carefully observing the correct electrical polarity (positive/negative) may result in damage to your Smartcast RF15 and your battery. If you are not comfortable with standard DC wiring alterations, please seek the advice of someone who is.

Step 1: We start by cutting the female end off of the extension cord about 1 1/2" above where the cord starts to coil.

Strip back the wires on the end of the female connector just enough to attach two female blade connectors to the exposed wires. The female blade connectors are a perfect match for the male blade connectors used as positive/negative terminals on the battery.

Make sure to observe the correct polarity of the battery so the positive (+) is at the center of the female connector and the negative (ground) is on the shell.

Here's a photo of the female receptacle attached to the battery. You can use a piece of red electrical tape on the positive wire to easily see which wire gets connected to the positive post of the battery.

Step 2:

Unplug the Smartcast RF15's power cord from the back of the fishfinder and trace the wire back to where it connects to the AA battery box under the units base. Clip both the positive (red) and negative (black) wires from their connectors on the battery box.

Strip back the wires about 1/2" and connect them to the matching wires on the end of the male extension power cord. Be sure to observe the correct polarity. You can use crimp connectors, but I recommend you use solder and heat shrink for a stronger connection.



That's it, you're done! Now attach the female receptacle to the battery. Then attach one end of the male power cord to the back of the Smartcast RF15 and the cigarette lighter end to the female receptacle on the battery. Turn on the Smartcast RF15 and put it in "Simulator" mode. Assuming the battery is fully charged, you have enough battery power to keep your RF15 working properly for several hours.

Here's a photo of the completed modification:

Note: You can't use a full-size car battery charger to charge this type of battery. It has to be charged at no more than 4 amps and it's better to slow charge it at only 2 amps.

The Black & Decker charger on your left is perfect for your needs here and if you are buying the battery and 12vdc extension cord from Amazon anyway, will make your order eligible for free shipping, saving you $10 or so.

This battery charger is much better quality than similar ones typically sold at auto parts stores and has a protection circuit to keep you from hooking it up backwards.

The author of this article is an avid fisherman and a partially disabled cancer survivor. Purchasing the items in this article from Amazon.com not only gives you the best prices available, it also helps the author earn a living.