Most important characteristics:

Inogen One G4 Battery (8 cell)

The Inogen One G4 doesn't have the long battery runtime of the G2 and G3. With this 8 cell battery, you can increase your mobility dramatically.

Charge and running time:

With the concentrator, you can charge one battery at a time. To charge multiple batteries, or separately from the concentrator, you can use the external battery charger.