Apple's iMac keyboard has a wireless Bluetooth connection, so it can be charged via a charging cable.
First, make sure the keyboard is powered off, then plug in the charging cable from the Lightning port on the bottom of the keyboard.
Next, connect the USB port on the other end to an iMac or other USB power adapter.
When the keyboard is charging, the small LED indicator on the charging line will blink and turn on when the charging is complete. The charging time is usually completed within a few hours.
After charging is complete, just pull out the charging cable and then use the keyboard. In this way, you can ensure that the iMac keyboard is always fully charged and ready to use.