I spent several thousand dollars on an oxygen concentrator. It is a POS. I'm having to send it back for repair, which will cost me 90$. A replacement "loaner" concentrator will be 400$, so I will be homebound over the holidays.The 6 hour battery lasts maybe 3 hours. The 4 hour battery lasts maybe an hour and a half. Every SINGLE word the salesman said to me was a lie. BEWARE!