In (3He,t) nuclear charge-exchange reactions, 3He+ charge states are produced as a result of atomic charge-exchange between 3He++ ions and atoms in the target. In equilibrium, the atomic charge-exchange process consists of both electron ionization (stripping), and electron capture, which can proceed through Radiative Electron Capture (REC) or Non-Radiative Electron Capture (NREC). Unfortunately, a complete description of the atomic charge-exchange process is lacking. As a result, a largely phenomenological approach has been used, which has not been tested for high beam energies. In this work, ratios of equilibrium charge-state yields for singly to doubly ionized 3He ions were measured using the Grand Raiden Spectrometer at the Research Center for Nuclear Physics (RCNP). A semi-phenomenological approach used when calculating atomic electron capture and stripping cross sections is successful in describing the data for beam energies of E(3He) = 420 MeV.