With the Philips Respironics SimplyGo Mini external battery charger, you can charge additional batteries outside of the concentrator while the unit charges another battery.  This gives you the ability to charge additional batteries to bring along with you and quickly swap out batteries while on the go! The external batteries are small and can easily be carried in either the SimplyGo Mini backpack or accessory bag. This external battery charger uses AC power and includes all the necessary cables. The external charger uses only 120 Watts of electricity while charging a battery.