Mega 360 ground wire

I just got my mega 360 in and I am making it portable so I can move between 2 boats. I am using fishing specialities mounts for the transducer. My question is where do you mount the extra strand ground wire or does it matter. I am powering it by a 20 volt craftsman tool battery as I rarely fish over 4 or 5 hours. Thanks for any help

Twist the black drain wire and black ground wire together and attach to the negative terminal of your fuse box or negative post of the battery. If you don’t attach the drain wire grounded,,your screws and wet switches are liable to rust.