Morgan did something very like this the night before Cowpens, going from one group of soldiers to the next and exhorting them. He had a little “stump speech” he would go through which culminated in him ripping off his shirt to show the scars on his back from a whipping the British had given him during the French and Indian War. (One whipping deserves another, I suppose, was the message of the speech.)
The immortal words of Prince Harry before the Battle of Bosworth Field: “Now I’m afraid that there’s going to have to be a certain amount of violence. But at least we know it’s all in a good cause, don’t we?” (As recorded in the historical recreation, The Black Adder.)
He wanted it to be “England confides …” (i.e., is confident). “Expects” was substituted because there was a single flag for it, whereas it would have been necessary to spell out “confides”.
…and, of course, maybe in ye olden days the troops were first gathered in a natural acoustical amplifier so the general could be heard.
…or the order was shouted down the ranks (this is where brevity is of utmost important).
…or someone just happened to hear the general’s remarks to his closest people and recorded it for posterity.
…or the general just wrote his own words himself later, after he comadeered a glorious victory.
The ultimate game of Telephone.
“Up, Men, and to your posts! Don’t forget today that you are from Old Virginia!”
"“Up and at 'em! Don’t forget today that you are an old Virginian. Purple monkey dishwasher.”
“What’d he say?”
“I think he said, ‘Blessed are the cheesemakers.’”
And/or a gathering of the commanders and lieutenants. For instance in the scene of old 'arry speaking on Crispin’s Eve, the setting seems to have him addressing a gathering of captains, NOT the massed ranks.
Hey, a historian who agrees with me. Always a good sign of accuracy in historians. 
Spoken by a man whose grandfather died in the Confederate Army, and who believed as a child that the portraits of Robert E. Lee and Stonewall Jackson were God the Father and God the Son. (Yes, he’s probably speaking for effect, but I think it’s ironic.)
I’m not sure that these can be classified as inspiring or as despairing words uttered by Jean La Valette, Grand Master, Knights of Malta, mid May 1565 before the Great Siege of Malta, before a gathering of all of his knights and lieutenants in the Cathedral.
Followed in late May 1565 by another inspiring? despairing? speech given to his fellow knights after hearing the bad news that reinforcements were not on their way, as originally hoped.
As it turned out, there was a happy ending, just like in the movies.
I was actually concerned nobody would read that link. It carries a lot of detail for the OP but suffers from poor presentation, whereas your contribution scores on succinctness and punctuality. You did, however, omit to mention one specific type of battle exhortation:
I bet he was embarrassed when he got back home.
“Guards Stand up” by Wellington at the battle of Waterloo.
Napoleons Imperial Guard were made up of the bravest,best trained and most experienced soldiers in the French army and had never been defeated in all of the battles of the Napoleonic Wars.
They were usually held back until the battles decisive moment and then sent in to finish hings.
At Waterloo the British Guards whom the Imperial Guard had never faced had been ordered to lie down by Wellington partly to lessen the heavy casualties being inflicted by the masses of French Artillery and partly to surprise the oncoming enemy.
After standing up the British Guards fired one volley into the I.G. and then bayonet charged
them,the shocked I.G. fled before them causing consternation throughout the French Army who had never seen them fallback in the face of the enemy and who in turn began a general retreat.
Their shout being Le Guard Recule!
Not a very glamorous speech but very effective.
To the honour of the I.G. when the battle was just about over and their shattered remanentswere asked to surrender to overwhelming force their reply was Merde!(shit) and they were then slaughtered by British Artillery.
Actually, I don’t think she agrees with you at all. Her concluding paragraph:
Emphasis added, link provided again (The historical reality of battle speeches) for convenience.
Exapno, the type of speech that you’re talking about, and that Staius Minatius was captured while delivering, is what Hansen refers to as a post-deployment speech. But Henoch provides evidence of more long-winded pre-battle, pre-deployment speeches, as well. For instance Hanno, with his army of mercenaries, was unable to stand before them and give them a good shouting to, so he gave the general message to the subordinate commanders and had them deliver the speech to their own units.
Someone upthread mentioned Gettysburg. The crowd for the various parts of the program is estimated at wikipedia as being around 15,000. I expect you have to speak from the diapragm for that type of oration… 
In looking again at the information on Queen Elizabeth’s speech to the troops at Tilbury, I find that it was “re-delivered” after she gave it. Here’s the letter of witness (and participant) Dr. Leonel Sharp on the subject:
And in the field of short exhortations, there’s Low Dog’s rallying cry at the Battle of the Little Big Horn: “This is a good day to die! Follow me!”
Patton’s actual speech was a lot more “colorful” than the one in the movie - he didn’t really say “fornicating” or “horse dung”. After reading it, I really, really, wish they had let George C. Scott use that version: “We’re not going to just shoot the sons-of-bitches, we’re going to rip out their living Goddamned guts and use them to grease the treads of our tanks. We’re going to murder those lousy Hun cocksckers by the bushel-fcking-basket.”
It doesn’t really apply to the OP though - he was speaking to the Third Army before D-Day, while they were still in England, so it wasn’t a “battlefield speech.”
Thanks for that link. I especially enjoyed this Patton quote:
“An army without profanity couldn’t fight its way out of a piss-soaked paper bag.”
Here are two good pre-battle messages, although the second was printed and distributed, not actually spoken to the troops in person:
“The time is now near at hand which must probably determine whether Americans are to be freemen or slaves; whether they are to have any property they can call their own; whether their houses and farms are to be pillaged and destroyed, and themselves consigned to a state of wretchedness from which no human efforts will deliver them. The fate of unborn millions will now depend, under God, on the courage and conduct of this army. Our cruel and unrelenting enemy leaves us only the choice of brave resistance, or the most abject submission. We have, therefore, to resolve to conquer or die.”- George Washington, Address to the Continental Army before the Battle of Long Island (August 27, 1776)
"You are ordered abroad as a soldier of the King to help our French comrades against the invasion of a common enemy. You have to perform a task which will need your courage, your energy, your patience. Remember that the honour of the British Army depends on your individual conduct. It will be your duty not only to set an example of discipline and perfect steadiness under fire but also to maintain the most friendly relations with those whom you are helping in this struggle.
"The operations in which you are engaged will, for the most part, take place in a friendly country, and you can do your own country no better service than in showing yourself in France and Belgium in the true character of a British soldier. Be invariably courteous, considerate and kind. Never do anything likely to injure or destroy property, and always look upon looting as a disgraceful act. You are sure to meet a welcome and to be trusted; your conduct must justify that welcome and that trust.
"Your duty cannot be done unless your health is sound. So keep constantly on your guard against any excesses. In this new experience you may find temptations both in wine and women. You must entirely resist both temptations, and, while treating all women with perfect courtesy, you should avoid any intimacy.
“Do your duty bravely. Fear God. Honour the King.” - Lord Kitchener, Field-Marshal, Guidance to British Troops (August 4, 1914)
Interesting points of emphasis from Kitchener. Was this the first time that Britain and France had fought on the same side?
England and France formed an alliance against Imperial Russia in the Crimean War (1854-1856).
I can’t think of an earlier occasion.