UPSs are designed to provide temporary power so attached computer systems and servers can be shut down properly to prevent data loss. UPSs are especially important in WANs. Because of the distance among links, sometimes reaching thousands of miles, WANs are more susceptible to power problems than LAN segments. Therefore, using battery backups to protect against fluctuations and outages should always be the first line of defense.

Although most central sites have UPSs, many remote sites typically do not, usually as a cost-savings measure. However, battery backup can be very inexpensive, costing only a few hundred dollars, which is cheap compared to the cost of indeterminate network downtime. Moreover, some UPSs have simple network management protocol (SNMP) capabilities, which lets network managers monitor battery backup from the central management console. For instance, every UPS can be instructed using SNMP to test itself once a week and report back if the test fails. The network manager can even be notified if the temperature levels in wiring closets rise above established thresholds.