Hard to see why leaving it on should bother it. I would check to see if you have low voltage from running down the battery. Electronics do funny things when they don't get enough juice. I had some electric company guys screw up the wires coming into my house once, everything read 120V but nothing would run, they had clamped a wire partly over insulation on the wire to the street. It had voltage but couldn't carry any amperage. Blew my furnace relay, and refrigerator. I've had a depth sounder on continuously for several day without problem so that alone shouldn't hurt it.