What UPS battery backup should I use with my system?
Generally speaking, you will want to use a Uninterruptible Power Supply (UPS) device, sometimes called a Continuous Power Supply (CPS) or battery backup, with a VA rating that is roughly 1.4-1.7 greater than your computer's power supply wattage. "VA" is short for Voltage-Amps and it describes how much load a UPS can handle.
This means for a system with a 400W-500W PSU, the minimum recommended VA rating for your battery backup device should be 700VA-800VA. Likewise, a 1200VA rated battery backup would be recommended for a PC with a 800W PSU.
Having an advanced battery backup in place to power your PC and LCD monitor (CRT monitors draw far more power and should not be connected to a UPS is possible) will help provide clean stable power for the daily operation of your system. In addition, it will allow you those few necessary minutes to safely save your working files and shut down your PC in the event of a power outage (blackout). It also protects against temporary power reductions (brownouts), transient increases in power lasting as much as a few seconds (surges), and intense split-second increases and decreases in voltage (spikes). So-called "surge protectors" only protect against spikes.