Just replaced my Gear S3 battery (24$ + 10$ for tools). Excited to get 3+ days back. Links in comments, will report back with new battery life in a few days. : r/GearS3
Amazon.com: LCLEBM 520mAh Battery for Samsung Gear S3 Frontier (SM-R760),Galaxy Gear S3 Classic Replacement Battery for SM-R770,BR760,R765,EB-BR760ABE Gear S3 Battery with Professional DIY Repair Tools : Cell Phones & Accessories
Official Samsung Galaxy S3 Extended Battery Kit - 3000mAh - Blue
100% Original Battery For Samsung Gear S2 3g R730 Sm-r600 Sm-r735 Watch Battery Gear S3 Br760 S2 Classic R720 R732 Gear S4 R800 - Mobile Phone Batteries - AliExpress
Amazon.com: hvoolee 450mAh Battery for Samsung Gear S3 Frontier (SM-R760, R770, R765), High Capacity Replacement Battery for Gear S3 Classic Internal with Professional Repair Tools : Cell Phones & Accessories