1st Kings 15 (and following) records many particulars on what went on during the days of Asa. However, here we have some additional details... very specific details, about Asa himself, particularly a few very disappointing decisions which Asa made at the end of his life.
As we saw in the last 2 chapters, Asa had done fairly well. For several decades, he had led Judah in the ways of faith and righteousness, but in his old age he resorted to his own ideas (instead of continuing to follow after God). It isn't really that he turned to overt acts of lewd wickedness, he just stopped leaning on the Lord. In his public, spiritual and private life, Asa took to contriving his own solutions to the problems that arose.
First, Baasha and Israel began to encroach into territory which Judah considered to be rightfully theirs. Now, Asa had seen what God could do on the battlefield... back when he had an encounter with the Ethiopians (2nd Chronicles 14:12). One would think that his past success would have caused him to follow the same strategy again; a strategy of dependence upon God 2nd I Chronicles 16:8). But no, he tried to handle this military threat by hiring Syrian mercenaries to defend his borders. Not God's way (2nd Chronicles 16:7). God wanted to help, but Asa got in the way instead of making a way 2nd Chronicles 16:9 & Isaiah 40:3).
Second. When God sent a prophet to rebuke Asa, he jailed him. Instead of humbling himself, he became and angry old man. And finally, when he contracted his last illness, he didn't ask God for help or health, he just went to his local medical clinic.