Unicron is the 1986 Animated film version, not the multiversal nonsense retconned into Transformers canon.
Batman is comics version.
Unicron is coming to Earth tear up its continents, which can potentially cause billions of death. Batman is the only one who can stop this because Unicron has imprisoned Superman in a red sun radiation prison inside of Unicron himself, and the rest are elsewhere fighting an intergalactic threat.
Batman however has notice of Unicron's impending arrival 1 year in advance, and he already has access to all resources and advanced technology in the Justice League watchtower besides his own regular equipment.
P.S: Batman can ask for help from Nightwing (Dick Grayson) and Red Robin (Tim Drake).
Question: Can Batman defeat or force away Unicron?