The Zen-O AC Power Supply is a major lifeline for your portable oxygen concentrator. You use it to recharge your batteries, power your concentrator overnight while you sleep, and use it when you're watching TV—it's a vital accessory for daily use. One of the more convenient features the AC power supply has to offer is that it can recharge one or two batteries at a time, as long as they are installed in your concentrator. Whenever you plug your Zen-O concentrator into the AC power supply, your batteries will begin to recharge and your concentrator will still continue to deliver your required oxygen. When it comes to recharging your batteries, the AC power supply is the fastest and most efficient way to recharge the batteries installed in your concentrator, taking only 3-4 hours to fully recharge one battery. The AC power supply is compatible with standard US AC power cords, as well as European and UK power cords, making international travel simple and easy. It plugs into any 110V wall outlet and provides quick battery recharge time.