The SD-9 battle droid represented a model from the SD droid series manufactured by Balmorran Arms, classified as a battle droid. Similar to its predecessors, the SD-9 possessed a humanoid form, but its size significantly exceeded that of even a standard Human.
This imposing SD-9 unit featured armor that could deflect lasers, shielding against ionization, powerful servomotors for movement, and sophisticated sensors for targeting. Instead of hands, its forearms were equipped with a heavy repeating blaster and a destructive plasma cannon. Rumor had it that this particular droid could single-handedly contend with a hundred soldiers. Furthermore, the SD-9 incorporated an ionization shield generator.
During the Thrawn campaign which took place in 9 ABY, the New Republic made limited use of SD-9 units. Later, in 10 ABY, during Emperor Palpatine's resurrected insurrection, the Empire successfully reclaimed Balmorra. Consequently, all remaining SD-9 droids were integrated into the Imperial forces. The Emperor also tasked Umak Leth, the mind behind the World Devastators and the Galaxy Gun, with collaborating with Balmorran engineers. Their joint effort resulted in the creation of the even more lethal SD-10 battle droid, which was ultimately turned against the Empire.
Following the Emperor's second demise at the Battle of Pinnacle Base, the Balmorran people initiated a rebellion. In response, the Emperor dispatched his executor, Sedriss QL, with the intention of suppressing the uprising, leading to the Battle of Balmorra. During this conflict, the SD-9 droids proved inferior when faced with the more advanced SD-10 models. The Balmorrans also deployed their new X-1 Vipers to counter Sedriss' Shadow Droids. The end result of the engagement was a stalemate between the opposing sides.