Battery pack including insertion guide groove with L-shaped opening

In the present invention, there is provided a battery pack including first to fifth terminal portions sequentially arrayed at one side surface of a housing, wherein the first terminal portion formed on one end side of the one side surface is a positive electrode terminal, the fifth terminal portion formed on the other end side is a negative electrode terminal, the fourth terminal portion formed adjacently to the fifth terminal portion is an ID terminal, and the fourth terminal portion and the fifth terminal portion are proximate to each other; and a guide portion for guiding the loading and unloading of the battery pack into and from a battery mounting portion is formed substantially in the center of the one side surface in array with the terminal portions, and the third terminal portion arranged centrally is formed at a position deviated toward the one end side or the other end side.