The Siri Remote has a rechargeable battery inside. With typical usage, you’ll need to charge it a few times a year. An alert appears on the TV screen when the remote battery is running low. You can also check the battery level in Settings.
Note: You can continue to use the Siri Remote while it’s charging.
Open Settings 
on Apple TV.
Go to Remotes and Devices, then select Remote.
Connect one end of a USB-C cable (sold separately) to the port on the bottom of the Siri Remote.
Connect the other end of the cable to a computer USB-C port or to an Apple USB-C power adapter (sold separately).
The Siri Remote takes about three hours to fully charge.
Connect one end of a Lightning cable to the Lightning port on the bottom of the Siri Remote.
Connect the other end of the cable to a computer USB port or to an Apple USB power adapter (sold separately).
The Siri Remote takes about three hours to fully charge.