Gear S3 Frontier vs Galaxy Watch3 - Technically it's a marginally thinner but smaller housing, narrower bezels, and weighs significantly less. It feels thinner than it looks, maybe due to the back
Amazon.com: for Samsung Galaxy Gear S3 Frontier SM-R760/ Gear S3 Classic SM-R770 Battery Replacement, EB-BR760ABE GH43-04699A Battery for BR760 R765 with Repair Tool Parts + Installation Instruction : Cell Phones & Accessories