A complete battalion of battle droids was under the command of the Separatist Alliance's T-series tactical droid commander TJ-55 during the Battle of Christophsis. This conflict took place in the first year of the Clone Wars, pitting them against the forces of the Galactic Republic. The battalion was composed of B1-series battle droids and received heavy fire support from Armored Assault Tank Mk Is.
Serving as a component of the Separatist Droid Army's army infantry corps, the battalion included numerous B1-series battle droids. Providing armored support were a minimum of seven Armored Assault Tank Mk Is. The battle droids within the battalion were equipped with E-5 blaster rifles.
A few months following the Clone Wars' commencement at the First Battle of Geonosis, the Confederacy of Independent Systems launched an invasion of Christophsis, a crystalline planet situated in the Outer Rim Territories. After rebels from the local area requested aid from the Jedi Order, the Galactic Republic deployed High Jedi General Obi-Wan Kenobi with his 7th Sky Corps, as well as Jedi General Anakin Skywalker and his 501st Legion, to provide assistance. As Senator Bail Prestor Organa organized a relief operation on the planet's surface, and Republic forces broke through the Separatist Christophsis blockade, Kenobi and Skywalker planned an ambush for the Separatist forces to shift the battle's momentum. By this time, the droid battalion was under the command of T-series tactical droid TJ-55.
However, unbeknownst to the Republic forces, Slick, one of their own clone trooper sergeants, had secretly switched his allegiance to the Separatist Alliance, giving them details about the Republic's planned trap. This allowed the Separatists to reverse the ambush against the Republic. Clone troopers from the Republic took up positions in two towers; Kenobi's group was in the south tower, while Skywalker and a small group of troopers kept watch from the north tower. Kenobi's troopers set up several laser cannons and kept an eye on TJ-55's battalion as it advanced towards them in several columns, followed by at least seven Separatist tanks. As the battalion got closer to the Republic's positions, Republic forces noticed that the battalion's troops were dividing into three columns. Shortly after, battle droids entered Kenobi's tower and caught the Republic troops off guard from behind, killing several clones who were unaware of the attack. With Kenobi's forces now surrounded within the tower, Skywalker had his men use ascension cables to cross over from their tower to help Kenobi, while also requesting an evacuation ship.
After Skywalker and his soldiers reached Kenobi's tower, they cleared one side of battle droids and joined forces with Kenobi. The remaining Republic forces evacuated using a lift to the tower's roof, fighting against TJ-55 and their battalion while they waited for the evac gunship. One clone trooper, Gus, succeeded in removing TJ-55's head, which allowed the Republic to analyze the tactical droid's databank and discover how the Separatists knew about their strategy. Ultimately, Slick was revealed as the traitor and was arrested, but not before he managed to destroy the Republic's arsenal.
The battalion made an appearance in "The Hidden Enemy," which was the sixteenth episode of the first season of the animated television series Star Wars: The Clone Wars'first season. It was broadcast on February 6, 2009.