And Rehoboam appointed Abijah the son of Maacah as chief prince among his brothers, for he intended to make him king.
See here, I. How Rehoboam was strengthened by the accession of the priests and Levites, and all the devout and pious Israelites, to him, even all that were true to their God and their religion. 1. Jeroboam cast them off, that is, he set up such a way of worship as he knew they could not in conscience comply with, which obliged them to withdraw...
Commenting on 2 Chronicles 11:13-23
made Abijah . . . chief . . . ruler among his brethren--This preference seems to have been given to Abijah solely from the king's doting fondness for his mother and through her influence over him. It is plainly implied that Abijah was not the oldest of the family.
And Rehoboam made Abijah the son of Maachah the chief, [to be] ruler among his brethren: for [he thought] to make him king. (g) Called also Abijam, who reigned three years, .