Jamieson, Fausset and Brown on 1 Kings 15:2

2. Three years reigned he--(compare 1Ki 15:1 with 1Ki 15:9). Parts of years are often counted in Scripture as whole years. The reign began in Jeroboam's eighteenth year, continued till the nineteenth, and ended in the course of the twentieth.

his mother's name was Maachah--or Michaiah (2Ch 13:2), probably altered from the one to the other on her becoming queen, as was very common under a change of circumstances. She is called the daughter of Abishalom, or Absalom (2Ch 11:21), of Uriel (2Ch 13:2). Hence, it has been thought probable that Tamar, the daughter of Absalom (2Sa 14:27; 18:18), had been married to Uriel, and that Maachah was their daughter.