When failure is not an option, the Premium Online Series UPS Backup Power Systems provide the cleanest power for mission critical, sensitive, and high-end systems. A completely isolated pure sine wave output provides perfect power free from noise and distortion for optimal system performance while the double conversion topology guarantees maximum system uptime. Front accessible batteries and remote IP management simplify maintenance and put you in control. The Premium Online Series UPS Backup Power Systems have a wide range of capacities, safeguarding any application. The expansion battery provides additional run time for the UPS-OL1500R model of Premium Online Series UPS Backup Systems Daisy-chain up to 10 battery expansion packs for longest runtime available in this form factor This unit requires one (1) UPS-OLRBP-3 AND one (1) UPS-OLRBP-4 replacement battery packs