Equipment Load: Line voltage and power.
Surge Protection Levels: Clamping Voltage, Response Time, Power Absorption (Joules and Amps)
Efficiency: This is a percentage, and the more % that is passed through, the higher the efficiency rating. A UPS uses some energy itself.
Surge protectors are limited in the amount of power that can flow through them and the amount of surge power they can redirect (Volts AC and Amps). The overvoltage when the protection starts is the Clamping Voltage. Maximum surge power ratings are rated in Joules and Amps. The Joules rating is a measure of the amount of electrical energy that the protection devices inside can redirect. The Amps rating is a measure of how much current can flow to ground during a spike. Surge protectors will help protect from induced surges from a lightning strike some distance away. Higher ratings indicate higher levels of protection. Direct lightning strikes near or at your building may produce pulses higher than the rating of any device - and start fires. [Data Backup and Recovery are other topics.]
In addition to Equipment Load and Surge Protection Levels, UPS maximum output power ratings are determined by the amount of power they can supply in the event of a blackout in Watts and VA (Volt-Amperes). The typical conversion formula from watts to volt-amperes is: volt-ampere = watts / (0.7PF). Consider buying a UPS that is rated higher than your equipment ratings to allow for peak currents and future growth. Exceeding the capacity means that there probably won't be enough power to keep you equipment running properly.
Output Waveform: Some sensitive electronics equipment requires an almost perfect sinusoidal waveform. The inverters in some standby off-line UPS produce a more rectangular wave or synthesized sine wave when supplying backup power. For most computer and electronics equipment, this form is adequate. The level of voltage distortion is often included in UPS specifications.
Battery Runtime and Life: UPS batteries have limited power and don't last forever. The time that a UPS can continue to supply power depends on the battery type, the efficiency and the load. Limits to battery lifetime mean that you'll need to plan to replace your UPS battery eventually. Manufacturers state a normal 4 to 7 year life span for sealed lead-acid (SLA) batteries. However, actual life may be reduced from heat and active use from outages.
See our UPS Battery Replacement Guide to find the battery that fits your UPS Model.
Reliability: Surge protectors and UPS are electronic devices. They have their own limitations and failure rates. You can reduce the risk of failure by choosing protection devices from manufacturers that use better design, better parts and better quality control.
***You can't eliminate the risks from power problems. Reducing them simply makes sense.***