Charge the batteries in wireless accessories
The Magic Keyboard, Magic Mouse, and Magic Trackpad each have a built-in rechargeable battery.
Check the battery level. Click the Control Center icon in the menu bar, click the Bluetooth icon , then choose the device.
Charge the battery. Connect your Magic Keyboard, Magic Mouse, or Magic Trackpad to your Mac or any USB power source with a USB-C to Lightning Cable or Lightning to USB Cable.
Tip: To charge the battery faster, be sure your input device is turned on when you connect it to your Mac Pro.