In all the sins of his father; which his father lived in; either, first, Before his humiliation. Or rather, secondly, After his deliverance from Shishak, when, though he did not openly renounce the worship of God, he seems to have relapsed into his former sins; which otherwise would not have been remembered against him; as David's name and memory is never loaded with the shame of his sins, because he truly repented of them.
Related Commentaries of 1 Kings 15:3
1 Kings 15:3
3 And he walked in all the sins of his father, which he had done before him: and his heart was not perfect with the LORD his God, as the heart of David his father.