System for producing an oxygen-rich gas comprising (a) a primary gas mover including a first and a second compressor, wherein the primary gas mover is characterized by a weight Wp (b) a drive motor adapted to drive the first and second compressors (c) a rechargeable power supply characterized by a weight, Wb and (d) a pressure/vacuum swing adsorption unit adapted to separate the pressurized feed air into an oxygen-rich product at a product flow rate Fp and an oxygen-depleted waste gas, wherein the adsorption unit comprises a plurality of adsorber beds containing an adsorbent and characterized by a total adsorbent weight Wa and wherein the combined weight, Wt, of the adsorbent, the primary gas mover, and the rechargeable power supply is characterized by the expression 0.75 Fp < Wt < 2.02 Fp where Fp is in liters per min (at 23 DEG C and 1 atma pressure), and Wa, Wp, and Wb are in pounds.
