Check your ground also. I fought with my 898 and 570 getting low voltage when cranking. I ended up running a heavier gauge wire for both the power and ground directly to the cranking battery. I cut all but about 24" of the Humminbird power cable off and soldered and heat shrinked this to my heavier wires coming from the battery. No issues since. Originally I had just ran a new power wire and grounded into the bus under the dash. Only when I ran the new ground wire as well did the issue go away. You could run a piece back to the battery temporarily to see if it helps before you go through the trouble of fishing the wires.

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