As electrified powertrains proliferate through original equipment manufacturer vehicle offerings, the focus on system cost and weight reduction intensifies. This paper describes the development and evaluation of a high voltage (HV) battery system enclosure molded from high density polyethylene (HDPE) to deliver substantial cost and weight opportunities. While previous battery enclosure alternatives to steel and aluminum have focused on thermoset composites and glass filled polypropylene, this solution leverages HDPE design techniques established for fuel tanks and applies them to a HV battery, with some notable differences such as employing two injection molded halves which are joined via infrared welding. The result is a tough, energy absorbing structure, capable of hermetic sealing, which simplifies manufacturing by eliminating nearly all fasteners. The authors evaluate performance with respect to crashworthiness, fire resistance, electro-magnetic compatibility and other challenges, by comparative research, computer analysis, and physical testing to demonstrate the system capabilities. The end result is a compelling argument for employing HDPE to enclose and protect a HV battery system, yielding cost and weight reduction opportunities over conventional solutions.