Bought a concentrator from this company. "Suppose" to be brand new. NOT. Its refurbished piece of crap. I was told one price then charged another. Called and emailed within the first 30 days. No one responded to me untill after the 30 days. Now they want their money. If I would of sent it back. Its has to completely in box and not opened. HELLO how ARE suppose to know if it works? You are taking advantage of people that have to depend on theses to help them breathe. A woman paid 3000 for a machine she never got. Another gentleman just wanted a new battery. Paid for it and never got it. DONT BUY FROM THE. CHECK THE BBB THEY ARE ON THAT SITE