A portable auxiliary unit for coupling with a mobile audio player is disclosed. The auxiliary unit provides both auxiliary power input and auxiliary audio output for the player, as well as a protective casing in the form of a receiving cup open on a top side. The receiving cup provides access to inputs and outputs on the audio player accessible by cabling from the auxiliary unit installed when an access panel is opened. The auxiliary unit has an integral rechargeable battery pack and a speaker assembly connectable to the audio player via the cables.