I'm a bit puzzled by all this talk of the battery voltage possibly causing so many problems. I could understand it if you were using rechargeable ones as someone mentioned earlier, the lower output of those when combined between 4 or 6 cells would make a difference but unless you put in some old duffers, the duracells should be absolutely fine and if the camera is so sensitive to such minor voltage variations, it's not worth having. Do you know of any other electronic device that acts so erratically - I don't. So as Paws says, it looks like you got a duffer mate. But good on you for persisting and trying different things. Does the device have a power socket that allows it to be run from an external source like a transformer? If so it would be worth trying it that way because that voltage would be consistent.
Wished I'd had one set up last week. As I arrived, I spotted a buzzard on the ground which flew up into one of my tree branches. Magnificent creature. There was a breeding pair somewhere in our woods this year. Later in the day I spotted three of them hovering just above my sycamore stand. I wonder if there's some way to entice them down to a place where a camera could be left to capture them. Hope they have an appetite for grey squirrel!
