Battery pack and the method of its manufacture

A watertight housing for receiving a battery comprising:

• a first half having a bottom wall, a plurality of side walls extending from the bottom wall, the side walls being continuous with each other at each of a plurality of corners to form an open ended closure for receiving the battery, each of the side walls having a top sealing surface at an end opposite the bottom wall, and electrical contacts disposed inside the closure and in communication with an outer surface of the closure, and;
• a second half being secured to the first half by ultrasonic welding to form the watertight housing, the second half having a seal disposed on an inner surface and inside at least one opening extending from the inner surface to an outer surface, the seal being cooperable with the sealing surface of the first half to prevent water from entering the housing while allowing gas to pass from the inside to the outside of the housing.