Originally Posted by rads
Our GPS (Lowrance LMS350A) has recently forgotten all the waypoints we have stored. I guess this means the internal battery has died.
Although this isn't a solution, it is possible to backup your user data(waypoints, trails, routes, icons,etc) on to your memory card on my LMS 320, so it may be possible to do the same on yours. It will at least prevent you from losing any more info.
Just go to Menu--System Setup--Transfer My Data--Save (or Load if you are restoring data you've previously saved)