The PLNK-series power droid was designed for storing and refueling liquid tibanna gas.[1] They were additionally built for refueling starships and equipment and performed simple tasks in spaceports and military bases.[2] To increase their capacity for tibanna, the droids were based on a "stretched" designed of the GNK power droid and had four legs, as opposed to the two of the GNK series.[1] Lacking both weapons and a programmed gender, the PLNK-series were equipped with feet that allowed them to waddle along.[2] They had a slow moving pace, weighed down by a heavy internal tibanna tank and tibanna-powered generator. A single unit carried an internal pump for loading and discharging liquid tibanna through its externally mounted hose and nozzle;[1] the fuel hose ran from the droid's left side to the nozzles holstered on its back.[4] Their actions could be controlled by a main panel for system diagnostics located on their front side.[2] The droids spoke a form of droidspeak similar to Gonkian,[3] saying "plunk" as they shuffled about and hence earning them the nickname "plunk droids." They also understood Galactic Basic Standard but were unable to speak it.[1]
Although unequipped with the near-limitless power generation of a standard power droid, each PLNK-series model possessed a tibanna-driven generator that was capable of supplying enough power to satisfy the needs of Republiclistening posts until its tibanna supply ran out.[1] Three plunk droids were enough to power a single listening post and could alternatively be used as detonators to destroy an outpost in case of enemy insurgency.[4] In the service of the Confederacy of Independent Systems, plunk droids were thought to have some defective circuits that led to miscalculation.[7] Like other power droids, plunk droids were encased in heavy shielding,[1] mainly over their fuel reservoirs,[2] and colored duranium plating[1]—ranging from dark green[3] to gray,[4] brown,[5] and gold[6]—to safeguard their highly flammable tibanna contents. To further protect their cargo, the units featured heightened security and safety protocols, but were still restricted by highly limited programming and artificial intelligence. The droids' self-preservation programming sometimes gave them cause to run away from their owners when "spooked" or agitated.[1]
A trio of plunk droids, containing liquid tibanna, served as the power source for the Grand Army of the Republic listening post Rishi Station on the Rishi moon, which was used to monitor a portion of the Outer Rim Territories for possible invasion by the Confederacy of Independent Systems. When Separatist BX-series droid commandoscaptured the station, the clone troopers manning the facility decided that it was necessary to destroy the installation to warn Kamino, the site of the Grand Army's cloning facilities, of the impending Separatist attack. The troopers rounded up the three plunk droid units[4] and wired them together[12] in order to detonate them using a thermal charge. When the remote detonator failed to sync up with the charge, clone trooper Hevy sacrificed himself to manually trigger the device, destroying the three plunk droids along with the installation.[4]