I am interested if anyone is having similar problems to me when an iPhone 3GS battery gets below 20%, i can just be generally using my iPhone then it dies on me. I have contacted apple about the issue and they have said that i should take the iPhone to the apple store and let them run some tests on the phone to see what the problem is. Then they probably want money to fix the problem!!!
I have tried various things such as restoring the iPhone and then setting up ad new iPhone but no luck, i have the latest firmware 4.3.4 and the problem still remains.

Could anyone give me some advise on what is the problem is and how i could possible fix it, if the iPhone needs battery change apple will do it!