MDHearing's charging cases for rechargeable hearing aids use a wall adapter which accepts 100-240V. The plug on the wall adapter is a standard NEMA 1-15P 2-pronged plug that can be used in any U.S. home.
However, if the hearing aid is to be used outside of the U.S. and Canada, a plug adapter would be needed for a 220-240V outlet. There is no need for a voltage converter.
