Here is a summary of the portable oxygen concentrators under ten pounds.
The Freestyle 5 is only 6.2 lbs and is small enough to carry at your side just like a handbag. It can also deliver up to 750 ml per minute of oxygen, and is considered a high capacity portable concentrator despite the fact that it's one of the small ones that don't require a mobile cart. Its dimensions are 4.4 inches wide, 10.7 inches high and 11.2 inches deep. It also has pulse dose settings between 1 and 5.
The internal battery lasts for around 1 hour on the highest setting, and around 5 hours on the lowest setting, give or take a few hours for the settings in between. Just give it around 3.5 hours while plugged into a power source to charge it back from 0% to 100%. You can also use the AirSep AirBelt to add even more battery life. You wear the AirBelt around your waist, and plug it into the Freestyle 5 when you need more time between charges. The AirBelt can be charged using the AC and DC power supplies, just like the Freestyle 5.