If you have multiple Inogen One G4 batteries then the External Battery Charger is a great option that enables you to recharge your batteries outside of the concentrator.

Custom-made for Inogen One G4 Batteries, this charger can recharge a fully depleted Single Battery in approximately 3 hours or a Double Battery in 5 hours. The External Battery Charger includes a Universal AC Power Supply with North American power cord for use in US and Canadian wall sockets. (A plug adapter may be needed to convert plug connectors for usage outside of North America.)

Usage Information: To use the External Battery Charger, simply plug it in and slide it onto your G4 Single or Double Battery. When the battery is in the correct position a solid red light will indicate the battery is charging. A solid green light will illuminate when the battery is fully charged. For complete instructions review the documentation that came with your equipment.