This review emphasizes the ion mobility in crystalline battery materials, encompassing both electrolytes and electrodes, and reveals a crucial distinction between their roles. Electrolytes act as ion conductors while maintaining the role of an electronic insulators to prevent the uncontrolled flow of electrons during battery operation. On the other hand, electrodes must serve as both ion and electron conductors to facilitate the recombination of ions and electrons upon their entry into the electrodes. Despite these divergent functions, from a quantum chemical perspective, the determination of migration properties depends on the minimum energy path connecting two equivalent intercalation sites and the maximum activation barrier along this path. This insight highlights the essential similarity in the migration behavior of ions in both electrolytes and electrodes, emphasizing the importance of understanding and optimizing ion mobility for the development of advanced and efficient battery materials.