I need a UPS for one desktop computer. I want to prevent computer rebooting when the electricity goes down and for this purpose I need to buy UPS. The back up time depends on the UPS or It depends on battery? I need to invest how much money ( including the price of UPS and battery) for the back up time of 1 hour for one computer? I will have to invest how much money if I need the back up time of 2 hours for one computer? I want to buy new UPS and new battery instead of used UPS or battery.