Portable gas fractionalization system

A battery pack for providing electrical power to a portable oxygen concentrator, comprising:

• a generally U-shaped body defined by a center portion and end portions, said center portion forms the bight of the U and said end portions form the legs of the U;
• a top portion, a bottom portion, an exterior side portion and an interior side portion;
• a longitudinal axis, said longitudinal axis is an axis that extends through the top and bottom portions and generally parallel to the side and end portions and passing through a wall of the interior side portion;
• a transverse axis, said transverse axis is an axis that extends through the end portions and parallel to the side, bottom, and top portions and intersecting the longitudinal axis
• a lower transverse axis, said lower transverse axis is an axis that is parallel to the transverse axis and passing through the bottom portion and intersecting the longitudinal axis;
• a central lower lateral axis, said central lower lateral axis is an axis orthogonal to the longitudinal axis and intersecting both the longitudinal axis and the lower transverse axis;
• a first and second end lower lateral axes, said first and second end lower lateral axes are axes which are parallel to the central lower lateral axis and intersect the lower transverse axis and which pass through respective end portions;
• a contact protrusion having two pairs of opposing sidewalls, at least one of the sidewalls extends from the bottom portion by about ⅜ or more, said contact protrusion having a first sidewall that is generally parallel to the lower transverse axis and has a length of about 1.5 inches or less, said contact protrusion having a second sidewall that is generally parallel to the central lower lateral axis and has a length of about 0.5 inch or less;
• wherein the distance between the exterior surfaces of the end portions measured along the lateral transverse axis is about 4.25 inches or less;
• wherein the distance between the exterior surfaces of the side portions along the central lower lateral axis is about 1 inch or less;
• wherein the distance between the exterior surfaces of the first end portion along the first end lateral lower axis is about 1.5 inches or less;
• wherein the distance between the exterior surfaces of the second end portion along the second end lateral lower axis is about 1.5 inches or less;
• and
• wherein the battery pack is substantially symmetrical about the central lateral lower axis and asymmetrical about the lower lateral transverse axis.