As other have said, it all resets from act to act.
And you don't need to pick up the battlefield keys and keep them in your inventory anyway. Just finding them and clicking on them to read the description is enough. (Unless of course you want to use Fire's very clever and sneaky trick to use the old keys for the new dungeons. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> Personally, I rather enjoyed the challenge of finding the new keys though.)
