Double the overall usage of the Respironics SimplyGo portable oxygen concentrator with the slim and lightweight external battery module, which will instantly give oxygen patients more freedom with what they can do with their concentrator. This accessory allows for patients to use a battery in the SimplyGo, as well as have an additional in the external battery module, giving them more time to enjoy friends and family. Using the module is simple—just slide a SimplyGo battery into the compartment, plug it in to the concentrator, and store it in the front zipper pocket of the carrying case. The external battery module is extremely intelligent in the sense that it knows when to automatically switch between batteries. The SimplyGo will first deplete the battery in the battery module and once that is fully drained, the SimplyGo will switch to running off of the battery in the unit. The external battery module is a must for oxygen patients that plan on flying, as the FAA requires all oxygen patients to have 150% of the flight time in battery life. Battery life with the module ranges from up to 12 hours on pulse setting 1 to 4 hours on pulse setting 3, and up to 4.6 hours on continuous setting 1. When a battery is in the external module it will not charge—you must slide a battery into the SimplyGo unit itself and charge with the AC or DC power supply.