Viewfinder 'dirty' when battery is depleted
I've run into a very weird problem with my Canon 7D. I forgot to check my battery and noticed it was depleted once I got to the location. The weird thing is that when I looked through the viewfinder it appeared to be covered by a grey-ish haze covered with transparent spots.
I switched lenses and the problem persisted, so I got home, recharged my battery and looked through the viewfinder again. The haze had miraculously disappeared and the image through the viewfinder looked perfect once again.
I took the battery out again, and the haze reappeared. So as long as I have a working battery in the device (the camera doesn't have to be switched on, just the battery needs to be charged), I'm not seeing the haze.
My big question is... is this healthy/normal and if not, what can I do about it? I assume it would be a problem with the mirror or the viewfinder's glass, since the problem persists when I switch lenses.