Batteries last for about 2 years, top of the line phones can easily last 4. They are after all made of glass, steel, and have plenty of ram. Take the Pixel XL

Batteries last for about 2 years, top of the line phones can easily last 4. They are after all made of glass, steel, and have plenty of ram. Take the Pixel XL from Oct 2016: 5.5 inch screen, 2560x1440, 4GB ram, quad core CPU, 128GB of storage. The pixel 3 XL isn't much different (same ram, same storage, 10nm CPU instead of 14nm). If apple keeps offering the $29 battery replacement I'd expect the average iphone owner will keep them for significantly longer. They already claim about $9B of losses because people are replacing batteries instead of buying $1k phone replacements.