Our site will have AC power available. Do we really need the internal battery pack?

It certainly is possible to power the system from AC, but I strongly recommend to our customers that they avoid any dependence on available utilities, and consider the camera system an independent element.

There are few places that will have 100% reliable AC power over the long period of an interesting project. Even places that have generator backup systems will have a momentary blackout, which can be enough to reset the DigiSnap timer. Battery backup AC units are certainly better, but it's much more efficient (power and cost) to power the electronics from a battery, and use AC or a Solar Panel to keep the battery charged.