Actually u can test the refurb phone before u leave the service center. I did that, found nothing wrong and left quite satisfied. Of cos, u can't test the battery life until u get home, but i think the refurb phone is supposed to come with a new battery.
If u are still not comfortable with exchanging, the cso will be able to diagnose whether the problem lies with the battery or ur software. For me, the cso scanned my battery and found that safari and a video app are the ones causing my battery drain. If i wanted to retain my phone, all i have to do is to reinstall the os and download the apps from scratch. But i chose to get a refurb set anyways.
Have some confidence in their refurb sets. I read alot of horror stories about defects but when i was there at the service center no one complained. Or u could try the reinstall os method first..