Charge your extra batteries overnight, while you are running errands, or even hitting the beach on your vacation, so they are ready to go when you need them. By allowing you to charge your batteries without plugging your concentrator in, the Oxlife Independence External Battery Charger adds convenience and peace of mind to your life. This charger is easy to use and notifies you when your battery is fully charged. Simply insert your battery into the slot as you would on your Oxlife Independence and a green LED light will flash, indicating your battery is charging. Once your battery is fully charged, the green LED light will be a solid light. If you feel like your batteries aren't lasting as long as they once were, the Oxlife Independence External Battery Charger has the capability of re-calibrating your batteries. Simply press the button on the charger and insert your battery. A solid blue LED light will glow until your battery is re-calibrated, then it will shut off.