see first look for ur req as oders suggested...anyhow the following terms will help u ....
Battery alerts. Most units have an audible signal, as well as a small light, to alert the user when power disturbances occur or when the battery is running low.
Cold start. This function allows you to use the UPS as a stand-alone power source without an AC connection, usually for a limited time.
Hot-swappable batteries. This feature allows you to change batteries while the UPS is in operation.
Run-time. The length of time the UPS will run (usually several minutes) to give you or the UPS time to close down computers and peripherals.
Transfer time. The length of time, usually measured in milliseconds, it takes for the UPS to take over the power operation of your equipment and switch to battery power.
Universal application shut down. already talked abt dat..
User-replaceable batteries: These easy-to-switch batteries eliminate the need to take your UPS to a dealer for servicing. An average battery lasts three years
finnaly the VA or volt ampere rating...its the amt of apparent power the ups can deliver....
compare ur choices on the basis of the above mentioned...