What are the…
Chronicles of King David
also known as: Annals of King David
These chronicles or annals, now lost to time, are mentioned in 1 Chronicles 27:24. Their author is unknown, whether it be one or more royal recorders or scribes, or possibly the contemporary Biblical prophet Nathan who seems to have written a life of David, and also a life of Solomon (1 Chr. 29:29; 2 Chr. 9:29), or possibly David’s royal seer Gad who is also known to have recorded events of David’s reign.
…David did not count those twenty years of age and under, because the Lord had said He would multiply Israel as the stars of heaven. Joab the son of Zeruiah had begun to count them, but did not finish; and because of this, wrath came upon Israel, and the number was not included in the account of the chronicles of King David. —1 Chronicles 27:23-24 NASB
They were likely statistical state records and one of the public sources from which the compiler of the Books of Chronicles derived information on various public matters.
Now the acts of King David, from first to last, are written in the chronicles of Samuel the seer, in the chronicles of Nathan the prophet and in the chronicles of Gad the seer, with all his reign, his power, and the circumstances which came on him, on Israel, and on all the kingdoms of the lands. —1 Chronicles 29:29-30 NASB