@stevelc Hi Steve, I had an Inogen 3 years ago . It never did work for me . I needed 4 ltrs and they did not have one for me . I am way happier with my even flow tank . The regulator on it is easy to use and I get all the oxygen I can use . Thanks . I am glad you enjoy yours . 3 hours is good on a battery . My tanks only last me 2 hours . I carry a spare in the car if I go out . I actually have a cart that will hold two tanks . I haven’t used it yet…. Apria is a great oxygen company . I use them too . I had some others , it is by far superior to all of them . Best to you , Crystalena