Traveled around Europe for 2 weeks with a dying iPhone 5 battery and a USB battery pack to boost it up, which worked quite well but looked strange dangling from the phone. Ordered a replacement from Amazon before I left and then installed upon returning. Unlike SteveMSflyer's experience @ the iStore, it took me all of 8 minutes to pry the old battery out and install the new one.

Next day, my wife emails me a link to Apple's replacement program, and I see that mine would have qualified had I not replaced it myself. Oh well, saves a trip to the iStore, waiting in line for a "Genius", then waiting for the replacement. The new battery works great, it now only runs down to 70 - 80% in a day's normal usage while with the old battery it was dead by 3 PM.