well I had a battle once as the HRE when I was taking over some territory in eastern europe , It was my first encounter with boyars ever.
3 full units of boyars + some other incompetent units they had , completely slaughtered my balenced army ( forgot the composition though ) while I only managed to destry 1 boyar unit.
The one thing to explain my loss was the fact that my general was lower ranked than theirs.