Features are disclosed relating to a case for a mobile device that provides supplemental battery power and supplemental storage space to the mobile device. Additional features are disclosed relating to an external storage device that can provide supplemental battery power and/or supplemental storage space for one or more devices. Further features are disclosed relating sharing and searching for files. Files may be shared across multiple (e.g., two or more) devices, operated by or associated with multiple users, providing multiple file storage locations. Files may be searched across the multiple devices using, e.g., search terms, tags, and/or other search options. Searching may also be performed with respect to activities performed in connection with subject files.