I have a deep cycle in the back of my boat that is used for all my 12v accessories. I have noticed while driving, seems like on take off mainly and in rougher water, the batteries voltage fluctuates from 12.1v – 9.8v. I am getting my voltage reading from my depth finder (lowrance hook 2). The battery is not connected to the motor or trolling motor, and has 2 leads running to a fuse panel under the console. The voltage seems to get low enough where my graphs screen will flicker on occasion while driving. Voltage returns to near constant once stopped.
Just looking for ideas as to what would cause this. Was thinking low water levels in the battery possibly? Pottentially a bad wire somewhere?