The Respironics EverGo AC Power Supply is one of your EverGo's lifelines. It is responsible for recharging your batteries while you are at home. Simply plug the AC power supply into any wall outlet and then into your concentrator and your batteries will begin to recharge. The EverGo AC Power Supply's main use is to recharge batteries. However, the AC power supply is able to not only recharge up to 2 batteries in the EverGo, but it will power the unit simultaneously. Whether you are watching your favorite tv show, reading a book, or playing some card games, the EverGo AC Power Supply will keep your batteries ready to go and your oxygen levels saturated. This essential accessory ensures uninterrupted oxygen therapy while keeping your batteries fully charged for when you need to go mobile.