I have a Garmin Legend and noticed when I put it on my truck dash weged in window I get a message that says lost external power then in 30 secs in shuts itself off. It does this wether I am using alkaline or nimh batteries. It also seems to do it when it is hot outside anyone else experience this? I have solved the issue by using the cigarette 12 volt adapter. So to me it is not just the heat but heat and a software issue? Anyone else experience this?