The AirSep 8-Cell External Battery provides you with another option to power your AirSep portable oxygen concentrator. It is compatible with all three AirSep portables: AirSep Focus, AirSep FreeStyle 3, and AirSep FreeStyle 5. Designed to fit in the upgraded AirSep FreeStyle 3 and FreeStyle 5 custom carrying cases or to be clipped onto your waist or belt, the 8-Cell external battery will provide you with a convenient way to supplement your battery life. The AirSep 8-Cell External Battery is meant to supplement your battery life and keep you up and running, allowing you to spend less time worried about recharging and more time enjoying your day. For the FreeStyle 3, expected battery life including internal battery ranges from 10 hours on setting 1 to 5 hours on setting 3. For the FreeStyle 5, expected battery life ranges from 7 hours on setting 1 to 2 hours on setting 5. Note: Focus adapter cable must be purchased separately to use the external battery with the Focus.