Because boating items don't get the road dirt and grease and oil fog that automobiles do,they may look great but in fact be worn out.
First things first. Charge the battery ,then take it to Advance auto or any parts dealer and they will load test it for free. If that is not possible,try hooking your troller up to your automobile battery..
Either of these options,should eliminate the possibility that the fault lies with the battery..If the battery checks out ok , or the motor refuses to run from the car battery,then a Minnkota repair facility is your best option.