A mobile phone apparatus is provided. The mobile phone apparatus includes a charger for supplying power to a rechargeable battery including a connection portion and a main telephone unit. The main telephone unit includes a rechargeable battery detection unit which detects whether the connection portion of the rechargeable battery is connected to the main telephone unit; an overvoltage protection unit which is coupled to the connection portion of the rechargeable battery and switches between an active state of supplying power output from the connection portion and an inactive state of not supplying power output from the connection portion; and a controller which controls the overvoltage protection unit to switch the overvoltage protection unit into the active state if the rechargeable battery detection unit detects that the rechargeable battery is connected.