UPS Hacking in Hurricane Season?

kengreenebaum asks: "Perhaps not the most exciting of topic; however it is storm season and I have a couple of UPS's that need new batteries. What is the best source for high quality, long lived replacement batteries for these devices? I assume it takes a special chemistry to survive continuous trickle charging and an occasional deep cycle. Has anybody tried connecting larger capacity batteries external to the UPS enclosure to attempt longer run times? (Obviously the load capacity is based on the inverter itself and can't easily be modified) Also what software do you use for monitoring and automatic shutdown on Linux? I have collected quite a few APC and Belkin UPS's 700VA or smaller as they go on rebate/sale."