It could be its just showing a more accuarate battery life! If your really worried about your battery life I use a app called Battery Doctor Pro for my Ipod Touch 2g and it works amazingly!
i updated my iphone 3gs with it. and i am shocked to see how fast its being drained. normally i can use it 2 / 3 days now beginning of the second day its totally drained. i also use a battery app but doesnt help at all. its so strange because normally an upgrade will improve battery life now its the opposite ! ps : i am a normal user. most games i play on my touch