I would think it would be a bad idea to plug a UPS into a UPS. A UPS would draw more power than everything that is plugged in to it would draw, therefore you would get fewer Amp/Hours out of your combined batteries. Now if you had 2 UPSs and only one device, then you could get a longer single uptime by putting them in serial like that but I assume you have more than one device to put on UPS.
[ August 22, 2002: Message edited by: VoidMain ]