This diary (which quite possibly may have been recopied from an original) ranges from Oct. 8, 1861 to July 12, 1862. There are numerous mentions of Cpt. Creuzbaur, but while the writer (Steussy) never mentions the name of his unit, he is directly under Cpt. Willke and certain Lt's as orderly sergeant which fits with Soldiers and Sailors and a 6th Tx Field Artillery muster roll I got from someone (waiting on the Tx State Archives for photocopies). Oct. 8th when the diary begins marks the date of assembly of Steussy's unit at the Capitol. They then proceed to Brownsville, are involved in fighting which I assume is connected to the French invasion of Mexico, and play an elaborate prank on a soldier (hopefully not Pfeiffer 8) ) which convinces him that a farmer's daughter desperately seeks to escape her father to marry the soldier.

I think the naming comes out of the fact the Cpt. Willke was promoted to Major in '62 and that the battalion formed in '64 was:

SEVENTH BATTALION, Maj. Sidney T. Fontaine, commanding.
Fifth Texas Field Battery, Capt. Charles Welhausen, 4 guns (mounted).
Sixth Texas Field Battery (Austin Light Artillery), Lieut. S. W. Allen, 4 guns (mounted).
Eighth Texas Field Battery, Capt. A. E. Dege, 4 guns (mounted).
Fifteenth Texas Field Battery, Capt. William H. Nichols, 4 guns (mounted).

according to http://www.couchgenweb.com/civilwar/artillry.html

So maybe Creuzbaur got promoted/shot and Welhausen took over.

I am going to begin transcribing the diary into Word this weekend and I will keep an eye out for Pfeiffer and Creuzbaur. BTW, I ran across a bibliography for Creuzbaur's unit on the USAMHI web page and in addition to the general stand by sources, it mentions "The Big Guns of Fayette" by Paul C. Boethel, 1965 as a source, and calls it "Creuzbaur's-Welhausen's Texas Battery".