As Camden was a horrific Patriot loss, there are not many books written about the battle. However, the old saw that the victors write the history is true with some of the best eyewitness accounts penned by British officers.
Cornwallis, Charles Cornwallis, and Ian Saberton. The Cornwallis Papers:: The Campaigns of 1780 and 1781 in The Southern Theatre of the American Revolutionary War. Vol. 2: […]. Uckfield: Naval & Military Press, 2010.
The primary source for British General Lord Cornwallis’s account of the battle.
Tarleton, Banastre. A History of the Campaigns of 1780 and 1781 in the Southern Provinces of North America. Dublin: Colles, Exshaw, White, H. Whitestone, Burton, Bryne, Moore, Jones and Dornin, 1787.
Also a good source for the actions that led up to the battle and its immediate consequences.
Piecuch, Jim. The Battle of Camden: A Documentary History (Amazon ebook: The History Press, 2006).
The Piecuch volume is akin to a primary source as it contains extracts from both American and British eyewitnesses (both officers and enlisted men). It is a good starting place to understand the battle and its consequences. Piecuch also summarizes contents of his book in a Journal of the American Revolution article.
Smith, David and Turner, Graham. Camden 1780: The annihilation of Gates’ Grand Army (Kindle Edition: Osprey Publishing, Inc., 2016).
Davis, Robert Scott, Thomas Pinckney, and William Johnson. “Thomas Pinckney and the Last Campaign of Horatio Gates.” The South Carolina Historical Magazine 86, no. 2 (1985): 75-99. http://www.jstor.org/stable/27567893.