There are 2 level 1 battlefield keys, so you don't have to worry about missing the first, though you can go back for it. The second key you will find shortly after getting out of the maze.
Go back past the trapped corridor and head west, then south and continue to the exit. There is a bit more to the maze, but it is not that elaborate, so just keep exploring and you will get to the end.
The first key... <span class='standouttext'>Spoiler : </span><span class='spoiler'>is in a chest on the southern walkway of the starting cell block, with the key in the left spider cage in the arena.</span>
