With the development and progress of technologies, various mobile devices such as mobile phones, panel computers, personal digital assistant and music players have become popular increasingly and bring great convenience and assistance for people's life. The mobile device generally obtains power from a rechargeable battery to maintain operation. However, the power provided by the battery of the mobile device itself is often very limited, particularly, the smart mobile device that rises in recent years with various functions has extremely large power consumption, and also has high power consumption rate, hence, the mobile devices generally confront the problem of short battery duration and high charge frequency. In addition, although the mobile device is typically provided with a built-in storage device, in certain cases, the storage capacity of such a built-in storage device still cannot meet people's requirement for data storage. On the other hand, in order to use and protect the mobile device better, shells for protecting various mobile devices dedicatedly have also been designed and applied. Some protection shells have also been designed to improve the appearance of the mobile device. However, such shells still play very limited functions. Therefore, the existing mobile devices still need to be improved in terms of performance, user experience, etc.