Battery pack

A battery pack comprising:

• a plurality of unit batteries each provided with a rectangular-solid shaped sealed type metal unit battery case and two voltage terminals, the unit battery case having two main surfaces which are larger than other surfaces and extend in parallel and the two voltage terminals projecting from one surface which is not the main surface of the unit battery case;
• at least one spacer, each disposed between two of the main surfaces of two of the unit batteries which are adjacent and opposed to each other so as to maintain the interval between the main surfaces;
• a connection unit which electrically connects the voltage terminals of different unit batteries;
• and
• two upper/lower plates disposed opposite to outside of the main surfaces of the unit batteries that are not opposed to the main surfaces of other unit batteries, wherein
• the spacer has a plurality of protrusions for supporting corner portions of each of the unit battery cases, and cut portions formed at positions opposed to the main surfaces which can receive inflated portions when the main surfaces of the unit battery cases are inflated by inner pressure of the unit battery cases such that the unit battery cases are aligned along the spacer and the voltage terminals are aligned in a common flat plane, one of the plurality of protrusions supporting two adjacent unit battery cases in the common flat plane and two adjacent unit battery cases in another common flat plane that is directly beneath the common flat plane;
• and
• the two upper/lower plates are opposed to the spacer with the unit battery cases therebetween, such that the two upper/lower plates do not contact each other, and the upper/lower plates and the spacer do not contact each other.