http://www.allelectronics.com/cgi-bin/category/160400/Gel_Cell_(Sealed_Lead_Acid).html

I use a SLA (Sealed Lead Acid, aka gell cell) battery in some of my homemade cameras. I use the 4ah battery and it lasts for months in the field or on the shelf.

I'm pretty sure it's that (or perhaps a smaller one) which the moultrie uses.

6 volt chargers can be had cheap at Radio Shack (or at least they used to be.)