Legend HCx unexplained shutdown

I made two 300-mile car journeys recently with my Legend HCx plugged into the car’s cigarette lighter socket. I saw during each journey that the GPSr had inexplicably shut down of its own accord. Can anyone explain this? The Track Log was set to ‘On’, 33% filled at most; the Track Log Setup ‘Wrap When Full’ is checked; the Record Method is set to ‘Auto’; the Interval was set to ‘Normal’ for the outward journey and ‘Least Often’ for the return journey; the Data Card Setup ‘Log Track To Data Card’ is checked. I had set a route using an uploaded gmapsupp.img from an osm_routable_gmapsupp extract courtesy of Lambertus, which appeared to be navigating correctly (as an aside, I do sometimes get ‘Route Calculation Error’ displayed in the course of my journey, for some reason). Even if there was a loss of power through the cigarette lighter socket for any reason, the GPSr would operate on its own batteries, displaying the ‘External Power Lost’ message, as it does when the engine is switched off. It is frustrating because it can be some distance before I recognise the GPSr has shut down, and the track data for that period is lost, of course.

Make sure you don’t have your HCx set to “shut down on power off”. I have a 60Csx and it’s an option on my unit. If you have just upgraded your firmware, you may find the upgrade has re-set your settings to factory default.