Battle Sky

Yes. Mark Romang's own site describes Battle Sky as the fourth and final installment of the Battle Series, and it is listed everywhere as "The Battle Series, Book 4". It closes the Tribulation storyline at Armageddon and the return of Christ.

Battle Scream, Battle Storm, Battle Siege, then Battle Sky. They are books one through four of one continuing Christian fantasy story, so Andrew Maddix's arc and the Mason family's situation both carry over from the earlier volumes — Battle Sky is the conclusion rather than a standalone entry point.