I use my Garmin 76s almost exclusively on the northern 1/3 of Kentucky Lake and I have never had such a problem with my unit. I bought one of the first units sold and use Fishing Hotspots. I can't imagine what your problem is. I can't verify south Kentucky Lake as I don't ever fish there. I use a mount. The only thing that I can think of is they will turn off if you lose your connection to the boat battery and that can happen frequently if you jostle the cord.

Ray