The M1 Air has separate battery and USB-C board guides; its memory and storage remain fixed configuration choices.
What to check before buying
Charging boards
iFixit documents replacement of the USB-C board separately from the main logic board. A port failure is a different parts job from a battery that no longer holds charge.
Battery and configuration
Battery replacement has its own guide. Memory and internal storage are not ordinary removable upgrades, so a used unit's capacity matters at purchase.