Charge the batteries in your accessories
Your Magic Keyboard with Numeric Keypad and Magic Mouse 2 each have a built-in rechargeable battery.
Charge the battery. Connect your Magic Keyboard with Numeric Keypad or Magic Mouse 2 to your iMac Pro with the included Lightning to USB cable. To check the charge level, click in the menu bar at the top of the screen, then choose the device.
Tip: To charge the battery faster, be sure your input device is turned on when you connect it to your iMac Pro.