These oxygen cells are the result of a seven year cell study, and are unique to the Apocalypse.  They are the same size as R22 or PSR 11-39 cells, with design changes to ensure the maximum reliability.

Oxygen cells are a controlled item: following your order, you will be prompted for your Apocalypse Certification Number, or a pre-Apocalypse rebreather certification number if you have ordered within one month of release (i.e. before 22nd Nov 2008)