WF-1000XM4. This listing is for the left earbud (L side) only. This is a used item, but the battery has been replaced with a brand new genuine Z55H battery, and has been tested and cleaned. You don't have to worry about the battery degradation that is common with this model. We have confirmed the operation, but if there are any initial defects, we will accept returns if you contact us before leaving feedback. Please check the photos for scratches and stains. For those whose one side has broken or been lost. The version is the latest 2.1.0. You cannot pair unless your device is version 2.0.0 or later, so please check your current version before purchasing. Pairing instructions for those who purchased only one side: Place both left and right earbuds in the case and insert the USB cable. It will blink red rapidly three times, then press and hold the touch sensors on both left and right earbuds (for about 10 seconds) until it blinks red slowly. Once it blinks red slowly, release your fingers. When it blinks green four times, initialization & pairing is complete. Delete the previous device information from the Bluetooth settings of the connected device and re-register.