One thing to note is that if everyone stops having children, it will create a demographic crisis with a lot of older people / pensioners not able to work and not a lot of working age people to support the aging population. Good for environment ofc but quite bad for the remainder of population.
To add, I think the batter capacity of a fairphone is 3905 mAh while eg Pixel 7 has 4355 so the diff is only ~10%
If I can replace a battery without throwing away the phone, I’d definitely be OK with 10% battery reduction