No idea about the level difference being a factor or not, but getting battle stones to drop from wild pet battles feels like running Heroic Auchenai Crypts for the Raven Lord Mount. In other words, pretty close to a waste of time. I think I've gotten something like 8-10 battle stones so far, and I ...

for as much as I'm concerned, I got a flawless one during a random battle (didn't take notice of what the enemy pet was), and an acquatic one against a strider in Blossom Vale. The 2 mechanic and the other acquatic one from sacks.