Cool-Lux MaxPower belts use nickel-cadmium (NiCd) cells that are voltage-matched for every belt. This is called cell balancing. Cell balancing allows all the cells to charge and discharge at the same rate, preventing premature battery failure. It is an expensive, time consuming quality check, but one that is extremely important. It ensures that every cell performs to optimal performance. The belt itself is virtually indestructible, and constructed with rugged, lightweight 1,000-denier nylon. Each is precisely cut and stitched with durable, condensed, heavy-duty thread to assure a smooth, tight surface with the cells firmly encased.