iFixit posts repair guide for Retina MacBook Pro, estimates battery replacement at $500 - 9to5Mac
MacBook Pro Battery Replacement Kits - 100% Apple Compatible
A1417 Battery for Genuine OEM MacBook Pro 15" Retina A1398 Mid 2012 Early 2013 | eBay
Amazon.com: A1417 Battery Only for (Mid 2012 & Early 2013) A1398 MacBook Pro - Replacement Battery for A1398 MacBook Pro 15-inch Retina (Mid 2012, Early 2013 Version) - EMC 2512 or 2673 [11.26V/99Wh] : Video Games
Amazon.com: E EGOWAY A1417 Laptop Battery Replacement Compatible with MacBook Pro 15 inch Retina A1398 Mid 2012 Early 2013, fits ME665LL/A ME664LL/A MC976LL/A MC975LL/A : Electronics
Replacing the Battery in a MacBook Pro Unibody (2009-2012) in 5 Minutes! - YouTube
Amazon.com: NinjaBatt Battery Replacement A1618 A1398 for Apple MacBook Pro Retina 15" [Mid 2015 Year ONLY]- Long Lasting [11.36V/99.5Wh] : Electronics
Mid-2012 Macbook Pro Battery Replacement - YouTube