An exterior power supply for a hearing aid has a battery-shaped conductor, two thin power contacts, and a DC power source. The battery-shaped conductor is received in a battery container of the hearing aid and has a top electrode and a bottom electrode. The thin power contacts are mounted to the battery-shaped conductor and respectively and electronically connected to the top and bottom electrodes of the battery-shaped conductor. Each thin power contact has a thickness matching a gap between an opening and a door of the battery container of the hearing aid. The DC power source is electronically connected to the battery-shaped conductor through a power wire and the thin power contacts to output DC power to the top and bottom electrodes of the battery-shaped conductor. Therefore, the hearing aid obtains DC power from the battery-shaped conductor and the button cell is not replaced frequently.