Volume key: triple click the right headphone button to increase the volume, triple click the left headphone button to decrease the volume.
Charging indicator/charging completed indicator: headset indicator (red when charging, full charge off) charging box indicator (charging frequency indicator of charging box flashes, full charge off).
The LED of the battery state during working indicates that when the battery voltage is lower than 3.3V (the battery capacity is lower than about 15%), the red LED flashes, and there is a prompt tone. When the battery voltage is lower than 3.1V (the battery capacity is lower than about 5%), the system automatically shuts down.
