BATTERY PACK

PROBLEM TO BE SOLVED: To enhance dielectric breakdown voltage by making cases connect easily with each other so as not to form a gap penetrating through a peripheral wall at connecting part connected by a locking nail. SOLUTION: The battery pack is composed of plastic cases 1 divided in a plurality of parts, secondary batteries 2, and printed boards 3 housed in the cases 1. The cases 1 divided in plural parts has a peripheral wall 4 formed integrally along a peripheral rim. The first case 1A has a plurality of locking nails 5 protruding inside from the peripheral wall 4. To the second case 1B, to which the locking nails 5 are connected, locking ribs 7 are formed protrusively on the peripheral wall 4 at the connecting position of the locking nail 5. The locking ribs 7 have locking parts 7A guiding and locking the locking nails 5, and one side of the locking parts 7A facing to the case 1 are blocked by blocking walls 9. The printed board 3 is installed at the inner surface where the locking nails 5 of the peripheral wall 4 and the locking ribs 7 are connected.