  Primordially formed extended dark objects would accrete baryonic matter and
impact the ionisation history of the Universe. Insisting on consistency with
the anisotropies of the cosmic microwave background, we derive constraints on
the dark matter fraction for various classes of objects, of different sizes. We
introduce a novel scaling technique to speed up numerical calculations and
release our calculation framework in the form of a Mathematica notebook.
Conservatively, we focus on spherical accretion and collisional ionisation. We
find strong constraints limiting the dark matter fraction to subpercent level
for objects of up to $10^4$ AU in size.
