For a full understanding of all the happenings in that time period, I would sugegst that you read ALL of the book of
Revelation 1-22 (KJV).
If you don't have time, then just concentrate on
Revelation 9-16 (KJV) and for specific information about the battle itself, use only
Revelation 16 (KJV).
If you wish to use a Bible version in a more understandable English text that does not corrupt the King James Version wording too badly, use the New Living Translation. (Click links below):
Revelation 1-22 (NLT)
Revelation 9-16 (NLT)
Revelation 16 (NLT)