My elderly father needed an oxygen concentrator to take with him on my parents' trip to Europe. The representative brought over an enormous unit on wheels with four very large additional lithium-ion batteries that altogether weighed around 30 pounds. My parents could not even carry it all; fortunately I was going with them and served as the pack mule. The representative took $450 which we were led to believe included a deposit, and we headed for the airport. The concentrator never worked right. It pumped as long as it was plugged in but the batteries never held their charge for more than a matter of minutes, even though they were supposed to charge while the unit was plugged in. My father had to do without it for most of the airplane flight, and could not take it with him anytime we left the hotel. Worse, when we returned and complained, the representative told us that indeed the unit was broken, but since we had actually taken the unit with us, we still owed the full $450 -- only then did we discover that this amount was not a deposit, but rather the full rental cost, for just six days! My parents were quite upset, and the representative offered to refund $250. So we were charged $200 for the use of a unit that did not work properly, that we could not use, and which nearly gave me a hernia lugging on and off of aircraft.