I have been unable to locate any information on Stephens/Stevens Artillery prior to the consolidation in late 1863.

This is the only find on the original unit:

Ritter's Company, Georgia Light Artillery
OVERVIEW:
Stephens Light Artillery was formed at Crawfordsville, Georgia, in September, 1861, with 165 officers and men. Its members were from Taliaferro and Wilkes counties. It served in the Department of South Carolina, Georgia, and Florida, then was assigned to J.Palmer's, J.W. Johnston's, and R.Cobb's Battalion of Artillery. The unit participated in the campaigns of the Army of Tennessee from Chattanooga to Nashville, then in 1865 aided in the defense of Mobile. During the fall of 1863 the 3rd Maryland Artillery Company was ordered to consolidate with this unit and in the spring of 1864 it totalled 108 effectives. It surrendered at Meridian, Mississippi, on May 10, 1865. Captain John B. Rowan was in command.

https://www.nps.gov/civilwar/search-battle-units-detail.htm?battleUnitCode=CGARITTCAL

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Ritter's Battery, Georgia Light Artillery
Stephens Light Artillery Capt. John B. Rowan
Capt. William L. Ritter
Originally this battery was the 3rd Battery of Maryland Artillery mustered into service 14 January 1862. It was reorganized in September or October 1863 as Stephens Light Artillery and the organization was credited to the State of Georgia.

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The artillery assigned to Potato Hill was Rowan’s Georgia battery, created by merging the Third Maryland battery with Stephens Georgia Light Artillery battery (named for Confederate Vice President Alexander Stephens). The captain, John B. Rowan, and the two section commanders, Lts. William L. Ritter and Thomas D. Giles, were all highly experienced veterans from the Third Maryland Battery. All four of their 12-pounder Napoleon cannons had been captured from the Federals at the Battle of Chickamauga and they had barely escaped across a burning bridge over Chickamauga Creek as the Confederates retreated from the Battle of Missionary Ridge. Their artillery could fire with accuracy up to approximately 1,500 yards, which meant that any Federal force within a mile’s range approaching from the direction of Varnell could be stopped by these guns. The well-directed fire from Rowan’s battery was often cited by Union commanders in their official reports of the engagement.
http://www.daltondailycitizen.com/news/local_news/civil-war-anniversary-the-battle-of-potato-hill-may-/article_6147b4d1-8552-57e4-94d7-d967aefe10cc.html