There is also ample medieval and early modern evidence for pre-battle motivational speeches. John Blise's study of high medieval chronicles found 360 orations spread across 92 Latin chronicles/histories from 1000 to 1250. Per usual with medieval sources, the recorded versions almost certainly do not reflect what was actually said. They would be more polished, flamboyant, and polemicized (for the purposes of the author of the chronicle, who might not always be a fan of the leader they are describing) than what was actually said. But as Blise points out, their themes and existence would have to feel realistic to readers. Some noteworthy ones:

The same points occur again and again:

• Appeal to troops' bravery and valor
• Appeal to belief in the cause (as sweeping as the Crusades; as petty as suppressing a town's armed revolt)
• The need to defend home, family, and land
• Mentioning the potential rewards (money from looting)
• Reassurance that God is on their side
• A reminder that they are probably going to die anyway, and wouldn't you rather die fighting that flighting? Yes, yes you would.

And of course, one of the most famous recorded speeches of all time, although naturally historians debate the connection between recorded words and proclaimed words, is Queen Elizabeth I's speech to the army at Tillbury, facing down the Spanish Armada and a potential invasion. (The Wiki article provides a few recorded versions.)

I answered this question recently here, garnished with a range of sauces.