APC Smart-UPS X 120V External Battery Pack Rack/Tower

Hot-swappable batteries
Ensures clean, uninterrupted power to protected equipment while batteries are being replaced

Rack/Tower convertible
Protects the initial investment in the UPS when migrating from tower to rack-mount environment.

Scalable runtime
Allows additional run time to be quickly added as needed.

User-replaceable batteries
Increases availability by allowing a trained user to perform upgrades and replacements of the batteries reducing Mean Time to Repair (MTTR)

Before purchasing check the battery compatibility: http://www.apc.com/products/family/index.cfm?id=152