How long does it take to recharge the batteries if they are completely depleted? Follow Approximately 13 hours. A separately available Quick Charger can be used to charge the external batteries in 5 hours. Helpful Links How Do I Purchase Accessories and Supplies? Related articles Can VOCSN run off of a generator? What configurations of VOCSN are available? Does bleed-in of external, low-pressure oxygen affect delivered tidal volumes and/or flow triggers? How Do I Use Leak Compensation? How Do I Provide High Flow Therapy?