The B1 Battle Droid, commonly known in-game as Battle Droid (not to be confused by different types of Battle Droids) or "Clankers" by clones in combat, is the primary infantry unit of the Trade Federation until the Battle of Geonosis where afterwards they became the backbone of the CIS and the basis for most of the other classes. Though their use greatly declined after the Clone Wars. In Star Wars: Battlefront, it was only playable in the first two missions of the Clone Wars campaign. It is not available in Star Wars: Battlefront II, where they were replaced by B2 Super Battle Droid as the main infantry unit. The B1 served as the basis for more specialized counterparts, such as the Assassin Droid, Engineer Droid, Assault Droid, ectara.
This unit is only available in the first 2 story missions of the Clone Wars Historical Campaign in Star Wars: Battlefront and is not available afterwards.
Many mods for Star Wars: Battlefront II (and, to a certain degree, Star Wars: Battlefront) attempt to include this unit in some way, usually by having it replace the Super Battle Droid and changing the latter to a more powerful unit.
It is odd that this unit is only playable in the story mode, especially since it is the most common CIS infantry droid in the Prequel Trilogy.
The B1 Battle Droid can be implemented into Star Wars: Battlefront outside of campaign mode by editing the "cis.lvl side" or have the "mission.lvl" read the B1 unit and replace the Super Battle Droid in the CIS stats.
The Confederacy of Independent Systems