A hearing aid adapted for placement on a head of a user comprising: a first part the first part comprising: an acoustic input transducer adapted to convert ambient sound picked up at an ear of the user to an electric signal, a signal processor adapted to process the electric signal according to specifications of the user into a processed electric signal, and an output transducer adapted to convert the processed electric signal into a transmission signal, a battery receiving area, and a second part, the second part comprising: an anchor adapted to fixate said second part under the skin to skull bone of the user, and a receiver adapted to receive the transmission signal and convert the transmission signal to an output signal perceivable as sound by the user, and wherein said first part further comprising an inner recess adapted to receive an insert element (30, 40), said insert element (30, 40) comprising a first magnet adapted to in cooperation with said second part to cause said first part to be connected to the second part by magnetic force acting through the skin of the user, and wherein the first part further comprises a cover system (90, 100) facing away from the second part when the first part is attached to the head of the user, characterised in that the cover system (90, 100) comprises a first section adapted to cover the first magnet, a second section adapted to cover the battery receiving area, and said first and second section locking on to the first part and with one another. a first part the first part comprising: an acoustic input transducer adapted to convert ambient sound picked up at an ear of the user to an electric signal, a signal processor adapted to process the electric signal according to specifications of the user into a processed electric signal, and an output transducer adapted to convert the processed electric signal into a transmission signal, a battery receiving area, and an acoustic input transducer adapted to convert ambient sound picked up at an ear of the user to an electric signal, a signal processor adapted to process the electric signal according to specifications of the user into a processed electric signal, and an output transducer adapted to convert the processed electric signal into a transmission signal, a battery receiving area, and a second part, the second part comprising: an anchor adapted to fixate said second part under the skin to skull bone of the user, and a receiver adapted to receive the transmission signal and convert the transmission signal to an output signal perceivable as sound by the user, and an anchor adapted to fixate said second part under the skin to skull bone of the user, and a receiver adapted to receive the transmission signal and convert the transmission signal to an output signal perceivable as sound by the user, and wherein said first part further comprising an inner recess adapted to receive an insert element (30, 40), said insert element (30, 40) comprising a first magnet adapted to in cooperation with said second part to cause said first part to be connected to the second part by magnetic force acting through the skin of the user, and wherein the first part further comprises a cover system (90, 100) facing away from the second part when the first part is attached to the head of the user, characterised in that the cover system (90, 100) comprises a first section adapted to cover the first magnet, a second section adapted to cover the battery receiving area, and said first and second section locking on to the first part and with one another.