surprisingly there isn't much info out there on this stuff. I got a 1KVA UPS here myself that needs to have the battery replaced. I haven't gotten around to it yet, but I think I am going to hook up a deep cycle marine battery to the leads and give her a test. The only thing I worry about is the inverter board and any overheating from extended use as a result of a larger battery.
"Fix it 'til it Breaks."

Jacob - EiC & Director of Technology
Mac Pro Quad 2.66 - 4GB RAM
160 GB SATA RAID 1 - 650 GB Storage
Quad 19" Widescreen LCDs
Accessorized to the Hilt