Buying one that doesn’t function as much as par is something, but you can even be buying one which doesn’t function in the slightest degree, or it’s just about to stop working. The seller may even present to plug inside the concentrator to tell you about that it really works. https://allhealthmarket.com/product/medical-supplies/portable-oxygen-concentrator-generator/oxygen-concentrator-machine-camping-use-oxygenator-driving-oxygen-bar-with-24-hours-battery-lasting-oxygen/