I know there is a bigger drain on the battery with 4G than 3G, but I can easily go at least a day and a half with a full charge with the Extended battery with medium use, even in 3G data. With WiFi, the thing could likely go 3-4 days.
One thing to consider... How long has the screen been on during this time? Yes, it will be the biggest drain, and thats a given due to its size. Looks to me like it could have been on for the majority of the time.
Right now I'm sitting at the following:
14hrs 30min since unplugged - Battery Level 49%
Voice Calls - 46% (1h 29m 41s)
Display - 39% (2h 40m 58s) most of it on 26%, a large portion on 50%
Cell Standby - 4%
Android System - 4%
Phone Idle - 3%
Wi-Fi - 2%
Android OS - 2%