army unit vs battalion

army unit and battalion both are nouns.

Word	Noun	Adjective	Verb	Adverb
army unit	Yes	No	No	No
battalion	Yes	No	No	No

As nouns, battalion is a hyponym of army unit; that is, battalion is a word with a more specific, narrower meaning than army unit:

army unit: a military unit that is part of an army
battalion: an army unit usually consisting of a headquarters and three or more companies

army unit (noun)	battalion (noun)
a military unit that is part of an army	an army unit usually consisting of a headquarters and three or more companies
	a large indefinite quantity