The nature of the dark matter is still a mystery. Upcoming 21-cm measurements during the cosmic dawn can provide a new arena on the search for the cosmological dark matter. This era saw the formation of the first stars, which coupled the spin temperature of hydogen to its kinetic temperature---producing 21-cm absorption. The strength of this absorption acts as a termostat, showing us if the baryons have been cooled down or heated up by different processes, such as elastic interactions with the dark matter. in particular, during the cosmic dawn the baryon-dark matter fluid is the slowest it will ever be, making it idela to search for dark matter elastically scattering with baryons through massless mediators, such as the photon. I will explore whether dark-matter particles with an electric "minicharge" can significantly alter the baryonic temperature, and thus affect 21-cm observations.