Looking inside an iPhone 4/4S battery | Rip It Apart - Jason's electronics blog-thingy
Battery for Apple iPhone 4S - by Raz Tech – Raz Technology (Pty) Ltd.
Mobile Phone Battery 1420mah For Iphone 4 Battery 4s Battery Replacement Батарея Для Телефона Original Batterie Bateria - Mobile Phone Batteries - AliExpress
SOLVED: Differences between 4 and 4s batteries - iPhone 4S - iFixit