If you're using an Apple TV 4th generation or later, you'll get a notification when your Siri Remote needs to be charged. Here's how to get it working again.
Apple TV 4K: How do I charge the remote and check the battery?
You’ll start seeing notifications on your TV once your Siri Remote’s battery reaches 20%. To start charging, plug one end of a Thunderbolt cable (you should have gotten one with your Apple TV) into the port on the bottom of the remote, then plug the other end into a computer’s USB port or wall adapter.
The Siri Remote doesn't have a physical indicator to show it's charging, but you will receive another notification on your TV that it's connected to power. To check the status and current battery level, check the menus on your Apple TV.
Open the System app from the home screen of your Apple TV.
