I have my Humminbird powered by my cranking battery and when I start the big motor it often draws down the battery enough and my 1198 shuts down.

I had considered just powering it off one of my three 12 volt batteries I have in my center console that power my 36 volt ipilot. Someone suggested that hooking into one of those batteries might not be good for the Humminbird because some of the voltage could bleed over or something of that nature.

So I am asking what to do. Could my cranking battery just be getting weak? It starts the motor fine. Anyone know of any downside to borrow a little 12V power from a 36V system?


Thanks in advance.

Yep...have your battery checked. Any autoparts store can do it, or better yet go to interstate directly. Good cranking batteries.

Is it ran straight to the battery or wired to a fuse panel or wiring harness?What size wire Sid you use

From what info I have gathered it seems powering a depth finder with trolling motor batteries can lead to interference on the screen when running the trolling motor. Guy also told me to spend the money and get a cranking battery with 1000 marine cranking amps. I think that should do it.

As long as you connect the depth finder across a single battery it will be fine. Be sure you use a dedicated pair of wires that go only from one battery to the depth finder. That is how I have mine wired in my boat and I have had no issues.

Run the power directly to the start battery and not into the boat's circuitry. You will not have the sonar unit reset on you when cranking and then get back to fishing.

I was having the same issues, I had my 1198, 998 and my 360, not running continuously, wired direct to my cranking battery. After 5 hours out on the water and running live wells and hydrowave, my units would shut down. I had a group 24 battery and I just upgraded to a group 27. The Group 27 has more reserve capacity.

Robbing power from a single TM battery:

1) Causes unequal drain on those batteries. If you are drawing any appreciable amount, that battery will eventually fail, prior to the other two in the set. This is a pain as batteries will give the best service life if you replace all 3 at the same time. You'll get out of sync doing what you ask about.

2) The TM is almost certainly digital pulse modulation controlled, and those emit a LOT of electrical noise. This is likely to give you pretty patterns on your unit's screen. You won't find it amusing.

3) If you have a Minn Kota US2 trolling motor model, and you use the battery with GND on it for the 36V system, you will blow a fuse inside the trolling motor. This is because your boat's 12V GND is never supposed to be connected to the 36V system's GND, per Minn Kota. I don't remember what fails if you blow this fuse.

4) I don't know if anything happens if you rob power from a battery other than the one with GND. I don't intend to try it; I have bad luck on things like that! Also, I know nothing about any concerns for Motorguide as I no longer use that brand.

Best solution: Do as many of us do, and get a big 'ol beast of a boat battery, often Group 29 or 31. Your problem will likely disappear, and you'll have good reserve. You'll need a new battery tray. There's a special one for Optima batteries if you go that route.

I agree with Flippin-Out. I run three units and a 360 all day long off my crank battery and have never had a problem.