Originally Posted by
arthurking83
Almost certainly something to do with LCD/powered assistance in the vf. Stuff like grid lines, focus points and so on.
That is, if the grid lines are overlaid onto the vf screen via an LCD screen, this LCD screen will need to be powered up to be viewable(and hence for the viewer to see the grid lines. When the batery power is removed, the grid lines become invisible, indicating a reverse polarity in the LCD(LCD's work the same way as a polariser does).
If the LCD is polarised one way so that the grid lines are viewable(say with battery power on), then it makes sense that the LCD is then reversed when power is removed and grid lines are now invisible. The LCD will become darker.
Grid lines and AF points use an LCD overlay.
Dunno how it works exactly, but you will notice how the crop lines also disappear with the battery removed.
D70s does this, so Mongo's hypothesis may be correct(in that all DSLR's do this). I thought they all did anyhow, ever since the D70s days.