For the PET, when the battle starts if I remember correctly, your CP determines your current power. when your CP goes up, you can have more access to battle chips, I have a collection and a Forte PET with a Blues casing (the thing with the glass window, it's removeable, not the pop-open one, the thing in the center of the casing, I had the forte, my brother had the blues PET).
Other than that there's the buster option too. Basically, the pad in the center is the D-Pad, and the two buttons above it are the menu thingies. My memory's real fuzzy when I last "operaited" this thing.