Charles Ellicott Commentary 1 Kings 15:1

"Now in the eighteenth year of king Jeroboam the son of Nebat began Abijam to reign over Judah." — 1 Kings 15:1 (ASV)

Abijam. —The form of the name given in 2 Chronicles 13:0, “Abijah,” is probably correct, as having a more distinct significance. The variation here, if not (as some think) a mere false reading, may have been made for the sake of distinction from the son of Jeroboam.