iPhone 4 warranty replacement

On Monday my phone that I got on launch day was damaged I made an appointment with a genius to discuss my options...anyway I ended up getting a different unit out of a plain black box, my issue is I am experiencing a very significant difference in battery life. Usually I charge my phone everyother day and with this replacement I am down to 50% 1/2 way through my day making no calls just a few texts and some minor browsing. Has anyone had this issue? What should I do?