sorry at this time no one has successfully changed their batttery, the N75 is just a battery hog. If you are not in need of UMTS data, then you can make the battery last longer:
1. Debrand your phone if you haven't. If you need instructions PM me.
2. Once your phone is debranded, you can go to settings>network>network mode and change from "dual mode" to
GSM.
3. Then go to connection>packet data and change from "when available" to "when needed".
This should give you a few more hours of batter life...you'll notice a difference.