I work in the medical field. Paramedic for 7 years and now doing cardiology at Loma Linda University Medical Center which consistently rates in the top 5 hospitals in the nation. Every doctor I work with uses an iPhone. Now I work in surgery so I can only speak for that, but I also know a couple of ER Docs and they use iPhones as well.
All that said, I don't really see the need for a removeable battery ( which is what they real topic is here, cause we all know the iPhone battery is easily replaceable ), because who really doesn't have the ability to charge while you're out or working if needed? But if you really feel the need to replace your battery throughout the day, carry a small Phillips screwdriver with you everywhere you go and open it up and replace it when needed. Yah, you may need a soldering iron as well, but I'm sure you have the pocket space where you usually carry all your extra batteries.
Or you could just get another phone and be happy.