I flashed my gf's Eris over to the v38 kaosfroyo and didn't purchase Setcpu, just running whatever kernel comes with the ROM. From a complete charge, the phone will last 2-3 hours with NO use. The only application that she is using that didn't come with the ROM is Fancy Widget. Its setup to update every 2 hours, so I don't see how that can be killing the battery. It also is very hot. It just acts like something is running and working the processor very hard. Any help? Maybe try a different ROM?