Ideal World:
If you turned off the Bluetooth, had a 5 bar service and did not touch the phone for texting or making calls you would probably get the standy time stated in the hand book.
Ah, we don't live in an ideal world:
If you have Bluetooth on - Constantly searches for things to connect to.
Low service level - Handset has to boost the antenna (using more power) to get a signal.
Software level - This could need updating or even a Battery/Handset recallibration.
All these things and more can affect the battery life of a handset.
Go visit you nearest Nokia Approved Service Centre.
Link for UK -
Nokia UK - Find Your Local Nokia Mobile Phone Store with our Store Locator
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