The rear cover opens to a user-replaceable battery; Fairphone also sells the display, cameras and USB-C assembly separately.
What to check before buying
iFixit score
10/10 · Rubric v2.1. Source: Smartphone repairability scores (iFixit). How to read the score.
Battery and screen
Fairphone publishes separate battery and display instructions. The battery is reached from the rear rather than through a glued screen.
Other modules
Fairphone also publishes camera and USB-C assembly instructions. The two long outer screws can damage the phone if tightened without the back cover in place.