The original total maximum inventory slots is 57 on the game disc alone after completion of both playthrough 1 and 2, but with the release of the Zombie Island of Dr. Not completing the missions in the first playthrough does not affect the chance of getting an SDU on the second playthrough. The appearance of the intentional nature of Playthrough 2 SDUs is the PC-confirmed program code that deliberately increases the chances of obtaining these 'random' SDUs if characters have less than 42 inventory slots already, or has more inventory slots filled when turning in the mission for the reward. Gearbox has not released any information confirming the additional SDUs to be glitches and they appear to be intentional 'bonus' SDUs that players have a chance of obtaining.

These additional Backpack SDUs are often referred to as glitches by players in Borderlands community forums. This can take several tries from either exiting without saving or loading from a backup file because the SDU reward is not 100% guaranteed. Unlike the first playthrough, only the first five of these missions (in the Sledge's Safe House, Lost Cave, New Haven, Tetanus Warren, Earl's Scrapyard locations) offer a chance of getting an extra SDU when completed. Once players complete the story playthrough 1, the higher difficulty playthrough 2 will allow them to repeat the Claptrap Rescue Missions for more Backpack SDUs. In summary after completion of playthrough 1 and the DLCs there is a guaranteed total backpack capacity of 48, with a maximum possible capacity of 51 (if Claptrap Rescue: Lockdown Palace provides a backpack SDU).

Completion of Claptrap Rescue: Lockdown Palace in The Secret Armory of General Knoxx has a chance of rewarding a Backpack SDU in playthrough 1 and is not guaranteed.

Ned, The Secret Armory of General Knoxx and Claptrap's New Robot Revolution DLC there are an additional 3 Claptrap Rescue Missions to complete.

With the addition of the Zombie Island of Dr. Each one is gained as a reward for completing one of the ten Claptrap Rescue Missions, for an extra thirty spaces of storage that can be earned throughout the game to a total capacity of 42 on the first playthrough. The Backpack SDUs each offer 3 additional slots of storage capacity. 3.2 Borderlands 2 and Borderlands: The Pre-Sequel.

Borderlands pre sequel gun slots