If you have the bolts projecting from the top of your battery (I assume all marine batteries do) then pick up a pack of ring terminals for you Hummingbird and a set for your trolling motor.
Ring Terminals
Take your wire strippers and remove about 1/4″ of the plastic sheathing to expose the bare copper wire. Try not to damage the wire when stripping. Next slide the wire into your ring terminal and crimp into place. I always use the heat shrink connections for wiring in my boat. Repeat these steps for your trolling motor and you will have a good, solid connection. $5 for parts and another $10 if you need a wire stripper/crimper is all this will take.
One other thing, if you don’t have your locator hooked up to a fuse bar, make sure that you wire an inline fuse to the positive lead on your Hummingbird. A 1-2 amp fuse should protect you.
Finally, I have had no issues running my locator off of my trolling motor battery. It is an older greyscale one so maybe that helps.
Any questions, fire away.