A battery casing used in an electrical device includes a box body, an electric sheet, a resilient electric portion and a switch apparatus. The box body for receiving a battery has a first sidewall and a second sidewall opposite to the first sidewall. The electric sheet mounted on an inner surface of the first sidewall is capable of electrically connecting with a first electrode of the battery. The resilient electric portion mounted on an inner surface of the second sidewall is capable of electrically connecting with a second electrode of the battery, and compressible to generate restoring forces. The switch apparatus mounted on an outer side of the first sidewall switches between a first position and a second position. When the switch apparatus is in the first position, the first electrode of the battery is detached from the electric sheet.