A mobile phone cover is provided comprising: a holder 120, 1120, 2120, 3120 for receiving and retaining a mobile phone 108, the mobile phone comprising an energy supply; a portable charging device 106, 1106, 2106, 3106 having two or more charging stations 110, 1110, 2110, 3110, each charging station 110, 1110, 2110, 3110 being configured and arranged for receiving and retaining a rechargeable instrument 104, the rechargeable instrument 104 comprising an energy storage; the portable charging device 106, 1106, 2106, 3106 being further configured and arranged: to transfer energy, in use, from the energy supply of the mobile phone 108, placed in the holder, to the two or more charging stations 110, 1110, 2110, 3110; and to transfer energy, in use, from the charging stations 110, 1110, 2110, 3110 to the energy storage of the rechargeable instrument 104 placed in the respective charging station 110, 1110, 2110, 3110. By providing a portable charging device in a mobile phone case, there is a reduced risk that an instrument will not work properly or be inoperable. There may also be lower chance that the user will forget to take the rechargeable instruments when they are travelling and/or away from home.