WF-1000XM4: The remaining battery charge varies greatly between the left and right earbuds

The battery consumption speed of each earbud is a bit different depending on each function setting and under what conditions you use them. It's expected behaviour. The numbers you see in the Headphones Connect app and given by voice guidance are estimates that can differ a bit. 

To minimise any differences, it's best to keep your earbuds safely tucked away in the charging case when you're not using them. 

If the wireless charging pad becomes too hot due to charging or because of the ambient temperature, the indicator of the charging case repeatedly flashes twice in red. This shows the temperature inside the charging case is too high, and the charging has stopped to protect the battery. When this happens, remove the charging case from the wireless charging pad, let it cool at room temperature, and then start charging again.

Tips for using a wireless charging pad

• Charging may slow down or stop, or the charging case may easily become hot if the charging case becomes misaligned with the wireless charging pad. For details on how to set the charging case properly on the charging pad, refer to the manual of the charging pad.
• When charging, remove anything attached to the charging case (e.g. cover).  Depending on the material or thickness of the cover or due to foreign objects caught between the charging case and the cover, charging may not be performed properly, resulting in fires, burns, or injuries.