Just got back from the shop, they plugged my phone in and ran the usual hardware software test, cameback as healthy.
Genius guy said they received an email from apple saying that, it might take a few charges for the batery to start holding more juice for longer, but he could see my point there, as i had a bit less than 2hrs of use today and about 6hrs of standby and my batery was already at 40%.
He gave me 2 options:
1. wait a few more days and see if the batery improves, if not go back to the store and replace the phone
2. replace my phone with a new one today
i've chosen option 2 as i couldn't be bother going back there and waiting another 30 mins stearing at the headphones for a new iphone.
So after 5 mins i had my new phone replaced, now i'm in the process of re installing all apps, contacts, photos... bla bla bla... phone came with 50% charge in it so i'll let it die first before i charge again... will bring more updates tomorrow...
cheers dan