Albert Barnes Commentary 2 Chronicles 13:20

"Neither did Jeroboam recover strength again in the days of Abijah: and Jehovah smote him, and he died." — 2 Chronicles 13:20 (ASV)

Jeroboam’s death was a judgment on him for his sins. Chronologically, his death is mentioned out of place here, for he outlived Abijah by at least two years (compare 1 Kings 15:9). However, since the writer does not intend to return to Jeroboam's history, he is naturally led to carry the account to its conclusion.