Should nav dvd player be constantly powered?

[erubus]

I am going to the TRNSMT festival in Glasgow today to see Radiohead so I went into the boot to disconnect the nav DVD player from the power so that my nav worked for glasgow city centre (hopefully hasnt changed much since 2003!)... It only works for a while before it just comes up as "nav not installed" on the MMI screen. Disconnecting it from the power and plugging it back in allows it to work for a while before reverting back to "not installed".

Anyway, the car has been parked up since about 1900 last night, this is Scotland so it is about 15 degrees and battering down rain, typical July weather. The DVD player was warm to the touch though. The rest of the computery looking metal boxes in that compartment were all cold though. This suggests to me that the DVD payer is continually powered, is this/should this be the case? Seems like a waste of battery.

gill