[Lucius Cornelius Sulla]

Could the other battle be when Merry and Pippin escape the clutches of the Urak Hai when the men of Rowan attack?

That was more of a big skirmish. In any case, up above, the suggestion was made that the battle was the taking of Orthanc by the Ents, which is only described, not shown, in the book.

[TigerTale]

In any case, up above, the suggestion was made that the battle was the taking of Orthanc by the Ents, which is only described, not shown, in the book.

And, I must say, I think if it was not shown in the movie, I would be disappointed. I want to see Treebeard and company tearing that place apart!