I work on the theory that I want everything running to finish whatever I'm doing. Save files, close programs etc. That means monitors, routers, dsl/cable modems, mouse/keyboard transmitters, external hard drives all have to be hooked up to a battery. The only things that aren't hooked to the batteries are a scanner, external speakers, and I think the printer (I'd have to follow the wires to be sure).

With all that, I found it better to have two backup power supplies on my main home system. I was more interested in the extra receptacles than doubling the battery life. Since I was going to have to buy another extension cord, I thought I might as well spend a few more dollars and get the real thing.