Are the battles in Macbeth good examples to explore the theme of violence and masculinity?
I would definitely want to argue that this is the case. I think one of the best parts of the play you can use to argue this is actually at the beginning of the play, in Act I scene 2, when Duncan is hearing the report of the battle between the forces of Norway and the treacherous Thane of Cawdor. Note how the exploits of Macbeth, who is called "Bellona's bridegroom," are conveyed:
For brave Macbeth (well he deserves that name),
Disdaining Fortune, with his brandish'd steel,
Which smok'd with bloody execution,
Like Valour's minion, carv'd out his passage,
Till he fac'd the slave;
Which ne'er shook hands., nor bade farewell to him,
Till he unseam'd him from the nave to th'chops,
And fix'd his head upon our battlements.
What is important to realise is that we have not actually been introduced to Macbeth yet. This, then, is our first introduction to his character. And note what a bloody, violent character he is presented as being. His blade smokes with "bloody execution" and he is reported to have violently and perhaps excessively killed the Thane of Cawdor, chopping him in two and beheading him. Yet note Duncan's response to this violent deed:
O valiant cousin! worthy gentleman!
It appears that from the beginning of the play such acts of gratuitous and aggressive violence are linked with an approved sense of masculinity. To be a "man" who is worthy of preferment and the King's notice, it is suggested, you have to be willing to perpetrate such acts of violence.