A DC adapter that can be housed in a battery housing portion of an electronic apparatus selectively with a primary and secondary battery. The sponge coating is made of a non-hydrogel polymer having a plurality of voids. Furthermore, the teleconference system takes into account that the potential invitees to a teleconference being scheduled can be different from one another in terms of their importance to a teleconference being scheduled, or in terms of the relevance of the teleconference to those invitees.