Hi Rob,
I should add to my post that I've set my D800 to display the image after shooting so I can chimp with a fast glance. Even set of time-lapse for 600-1200 images, I still have ample battery power with the D800. The big killer is when you do dark-field subtraction for long-exposure noise reduction.
Two batteries and 150-300 photos per day, a second battery may be all you need for now.