i agree with casketizer. the fone just shows the 2.5g availability and doesnt use any extra power than 2G. My fone shows 2.5G too and battery works for minimum a day with wifi usage as well as some hours of music playback.. you need to reflash your firmware and emmc ..that should defo solve ya problem.. if it doesnt ..its time for a new battery !

you can also try boostn900 script, for better battery ..
http://talk.maemo.org/showthread.php?t=63997