It's quite easy to replace the battery yourself. You can buy a kit with a battery and all tools, follow the included instructions, watch a video tutorial if you need.
It's a huge advantage for bike touring: I can charge this thing with a dynamo in a couple of hours because the battery is only 1600mah. That's less than a third the size of the battery in the current Pixel 6/6 Pro.
https://support.apple.com/iphone/repair/service/battery-powe...