A high-capacity battery pack attachable to a small-sized electronic device in which a lithium-polymer cell and a lithium-ion cell are physically coupled and to be electrically connected in parallel, and an electronic device using the battery pack maximize a battery mounting space while providing a high-capacity battery pack useful for the small-sized electronic device. The battery pack is arranged such that the lithium-polymer cell having a thin thickness in a large cross-sectional area and a lithium-ion cell having a thick thickness in a small cross-sectional area are appropriately arranged to maximize the space of the battery accommodating portion.