An electric power control method and a mobile device adapted thereto are provided that stores power for subsequent provision to a Subscriber Identity Module (SIM). In exemplary operation, both an RF communication unit and a charging unit are operative. The charging unit is coupled to a SIM electric power supply and the SIM. Upon occurrence of a voltage drop in the electric power supplied to the SIM, there is a switch to the charging unit to supply the charged electric power to the SIM.