It seems it helps reviving old threads now and then, they get more attention the second time around I got an e-mail from a friend I haven't heard from for ages saying his son found my article on the net.

You guys must bear in mind that when I did the initial test after installing the UPS I had everything maxed out on 2 computers where the CPU's were running 100% the graphics cards were working hard, the wireless router was under load and I had a huge 3-in-1 lazer scanner/copier/printer spewing out pages of print. (Lazer printers and UPS don't mix so I wouldn't recommend anyone runs one off the UPS unless they rated to handle it)

With our recent power outage I shut down all the peripherals and only had 1 PC and monitor going. The CPU was still at max load and the graphics card was working hard for some of the time. I got over 5 hours out of. I'm quite sure that if I had another set of batteries wired in parallel I could get a straight 10 -12 hours out of it. That supports what airmon has said. (great post BTW)

The batteries I used were deep discharge and recommended for a UPS. However as someone suggested to me the other day, if you used a car battery, there's nothing stopping you from popping it into the car and going for a drive around the block to recharge it. That way if you had a spare, you could have an endless supply of power