I want to buy an extra battery for the concentrator, but for some reason TTLife won't process the purchase. It almost seems that in order get a 2nd battery, I have to but another concentrator. I also have 2 Inogen one concentrators , bought through Main Clinic Supply. A simple phone call to them is quick, easy and gets me what I want or need, Too bad TTLife doesn't work that way. I like the features of the 08G, but my wife requires 4 or more L/Min when we're out shopping.