As I said, a different approach is much easier....
To confront Balthasar while he still is in the temple. He doesn't spawn his army of undeads there and you only have to deal with his guards. He went down within two rounds. Interestingly, the ensuing boss fights, including that Orc woman were much easier. Gale and Halsin casting ice storm had her down in round one. Same with Kethric Thorm and the monster he turns to.
