iPhone Diagnostic Tool in Support Page?

Went to the Apple Store in Holyoke, MA regarding battery issue. Specifically, iPhone 5 performs a hard shutdown at around 30%. The Genius Bar Tech ran a diagnostic which confirmed my issue. He then gave me a replacement iPhone 5 running iOS 6.1.4 (at my request) since I believe the issue is with iOS 7.0.3. He mentioned that the Apple Support page has a link to a diagnostic tool that I can document my findings. Problem is, I don't see the link anywhere. Can anyone help? Thanks!