Inogen One G4 Double Battery can last up to 5 hours at a flow setting of 2 when it is fully charged. The G4 rechargeable lithium-ion single battery is a perfect power source to give you independence and mobility for trips or other activities. The double battery will also fit comfortably in your G4 carry bag or in most accessory bags or purses. The Inogen One G4 Battery can be charged in under 4 hours and will charge while the unit is connected to an AC or DC power supply. It can easily be charged with the Inogen One G4 External Battery Charger.