I always thought that using a conventional UPS with a PC is highly inefficient. Power goes from AC -> DC -> AC in UPS and then AC -> DC in PC SMPS. Since PC works only with DC (12, 5 and 3 volts) It should be possible to convert AC -> DC once and use that to charge SLA battery and drive a PC.
Sure enough there are solutions for this. For example PicoUPS-100. These are designed for embedded PC, but I see no reason why such a device cannot be used for home PC also. Place where I live has frequent power outage and if I can hookup couple of battery with such a system it would give me long battery backup time with minimal cost if I use a power efficient PC.
Does any one have any experience with such systems for a mainstream (home) PC.