Inogen One G4 External Battery Charger with Power Supply is the ideal power source for recharging your Inogen G4 single and double batteries. Batteries can be easily charged outside the G4 unit in under 5 hours using this charger. A fully depleted G4 single cell battery will completely recharge in 2.5 hours while a fully depleted G4 double cell battery will be completely charged in under 5 hours!