zDock® CI821UDA Desktop Dual Charger Set for the Cisco 8821/8821-EX Wireless IP Phone charges your phone and a spare battery at the same time. It keeps your batteries charged, ensuring that your phone is ready for continuous use over an extended period of time, so you will never have to worry about running out of power again. Not only that, it features our patented Dock-in-Case Solution, which lets you dock your phone with or without the zCover case on. It also gives you full access to the keys and screen so you can keep using it while charging.