iFixit's Do-it-Yourself iPhone Battery Replacement Kits to Remain $29.99 Until End of 2019 - MacRumors
iPhone 6 Plus Battery Replacement - iFixit Repair Guide
Amazon.com: High Capacity Compatible with iPhone 6S Plus (5.5") Battery Replacement, Upgraded Battery for iPhone 6S Plus A1634 A1687 A1699 with Professional Repair Tools Set : Cell Phones & Accessories