"All UPS systems require regular intervals of maintenance. The availability of a system configuration is dependent on its level of immunity to equipment failure

"All UPS systems require regular intervals of maintenance. The availability of a system configuration is dependent on its level of immunity to equipment failure, and the inherent ability to perform regular maintenance, and routine testing while maintaining the critical load. As the configuration goes higher on the scale of availability, the cost also increases." (APC White Paper 75)