Well, I managed to do it in pretty much every single battle, even on impossible. There were a few tough battles where I didn't manage to do it fully, but that is to be expected.
Here's my battle stats. I'm sorry for the sloppy cutting and pasting in Paint, but that was the fastest I can do on such short notice
NOTE: 150 battles is what I did so far. I'm just getting to the orc lands, so my +int medal is about to rise.