Mercenaries just helped me keep Prussia. I hadn't been checking my provinces when suddenly Prussia revolted with an army of 1300 rebels (I'm the Portuguese so Prussia is far off from the rest of my empire). My troops held off that rebellion but with significant casualties. My army consisted of Russian troops that had rebelled in a Russian civil war so I cannot replace any casualties. The turn after I fought off the rebellion the Lithuanians reappeared with 4000 troops.

As I had only 212, it did not look good. I considered just retreating and ransoming them but I checked what mercenaries were available and decided instead to have a major last stand. I trained some Slav Warriors and hired all the mercenaries available. It was my 592 troops versus 4000 Lithuanian savages. My troops were just a bit better in quality but vastly superior in valour. My men fought valiantly and crushed wave after wave. I defeated the last wave just in time because I don't think I would have survived another. My troops were exhausted and depleted but I won with just over 300 casualties. My general of this battle received some very nice traits and also went up from four stars to six. The mercenaries helped to kill nearly all the enemy troops. The only downside is that I didn't get the Butcher trait. I ended up with about 970 prisoners and just missed the mark.