Enjoy the freedom to recharge a depleted EverGo battery without the need to plug in the AC or DC power supplies. Instead, the one bay Respironics EverGo external battery charger offers its own 110v AC supply so you can externally charge a battery wherever you are. Instead of having to wait for individual batteries to charge in the EverGo with the AC power supply, externally charging a battery will allow you to accomplish necessary tasks and when you return there will be a fresh fully charged battery waiting to be used. As an added feature, the Respironics EverGo external battery charger will not only charge your EverGo batteries but it will also recalibrate them. Recalibrating your batteries resets the lithium ion cells so they effectively hold as much of a charge as possible, with the calibration process taking approximately 8 hours per battery. An internal cooling fan keeps components from overheating. The LED indicator shows charging status (flashing green for charging, solid green for complete, solid red if battery needs replacement) and calibration status (flashing blue for recalibrating, solid blue for complete, solid red for error). The charger weighs 2 pounds and measures 3.5" W x 7" L x 2" H.