There are two different inserts that slide into the battery grip. One holds the lithium batteries and the other holds the AA's.
You put 4xAA batteries into the BP-220 battery pack (it doubles as a vertical grip w/ extra shutter release button) and the battery pack plugs into the K2. You'd have to remove the battery compartment cover so that the BP-220 can be inserted and installed on the bottom of the camera.
