Went to Office Depot and salesman tried to sell the largest size APC unit they have, but cannot seem to tell me why I need 1000, as opposed to a 700, 650 or 500 unit.

I will be plugging in 3 computers, only two of which are on at a time, the monitor and miscellaneous other electronic devices. I am seldom more than 5 minutes away from the office, in the event of a power loss. So, I do not need a battery backup to provide 30 minutes of back up. I need 3 to 5 minutes to allow me to shut down the computers I am using, in the event of a power loss.

Do I need more than a 500 unit, for my protection?