The National Archives in their Microfilm of Military Service Records, holds in Microform M269, Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Mississippi. Records for the 7th Mississippi Infantry are found on Rolls 159-164.
Separately on rolls 165-167, we find the records for the 7th Infantry Battalion.
Thus, it would appear, that these were two distinct units.
Checking the US Army Military Hisotry Institute at Carlisle Barracks, they also list two separate units. For the 7th Inf. Batt., they refer to:
Crute, Joseph H., Jr. Units of the Confederate States Army. Midlothian, Va: Derwent Books, p. 170 for "A consise summary of the battalion's service."
and, Sifakis, Stewart. Compendium of the Confederate Armie: Missisippi, NY: Facts on File, 1995. pp. 82-83.
Have you tried a Goggle Search: "7th Mississippi Infantry Battalion"?