Inogen One G2 desktop charger for external batteries. Recharge your Inogen One G2 Battery with the Inogen One G2 External Battery Charger. Custom-made for Inogen One G2 Batteries, this recharger can recharge a fully depleted battery in approximately 4-hours (12-cell battery) or 8-hours (24-cell battery). The External Battery Charger includes an AC Power Supply with North American standard power cord for use in US and Canadian wall sockets.