  The semiconductor BAs has drawn significant interest due to experimental
reports of simultaneous high thermal conductivity and ambipolar charge
mobility. The \textit{ab~initio} prediction of high electron and hole mobility
assumed the dominance of charge carrier scattering by one phonon. Recently,
higher-order electron-phonon scattering processes in polar and non-polar
semiconductors have been reported to have a non-negligible impact on charge
transport properties, suggesting they may play a role in BAs as well. Here, we
report an \textit{ab~initio} study of two-phonon electron and hole scattering
processes in BAs. We find that inclusion of these higher-order processes
reduces the computed room temperature electron and hole mobility in BAs by
around 40\% from the one-phonon value, resulting in an underestimate of
experimental values by a similar percentage. We suggest an experimental
approach to test these predictions using luminescence spectroscopy that is
applicable to the defective samples which are presently available.
