The Eaton 9PXEBM72RT2U 9PX 2U Desktop/Rackmount UPS Extended Battery Pack is an extended battery module designed to provide extended runtime to an Eaton 9PX 9PX1000IRT2UBS and 9PX2200IRTNBS UPS. You can add up to four (4) external hot-swappable battery modules, which are able to run systems for hours if necessary. Comes with a rackmount kit.