Tony,, how long is the batt lasting ??,, when mine was new (XDA2), would only last 6-8 hours,, now it run! in, last a couple of days, depending on use !!
With mine in the Bob, also connected to 12v via cig lighter, stays on all the time,when the ign off, the unit shuts down,,
Check "settings" System" Backlight" Battery power" have mine set to switch off after 1 min when on battery, and allways on when on external power,,
Would think you unit would be simalar
Works for me !!