fighter vs battler

fighter and battler both are nouns.

Word	Noun	Adjective	Verb	Adverb
fighter	Yes	No	No	No
battler	Yes	No	No	No

As nouns, fighter and battler are synonyms defined as:

Other synonyms of fighter include belligerent, combatant, scrapper.

fighter (noun)	battler (noun)
a high-speed military or naval airplane designed to destroy enemy aircraft in the air	someone who fights (or is fighting)
someone who fights (or is fighting)
someone who fights for a cause