Well, I am only three years late and guess you probably have your answer by now, but there is a diary by Sgt. Eggleston of Cowen's Battery found here: EXCERPTS FROM THE CIVIL WAR DIARY OF E. T. EGGLESTON by Edward Noyes in the Tennessee Historical Quarterly, Vol. 17, No. 4 (December, 1958), pp. 336-358. I have a copy if you need any further information from it.
Best,
Sue B. Moore