You can check the battery level in two different ways when the headset is powering on.
When the headset is powering on, the red LED flashes rapidly indicating the battery level.
4 flashes = High, 70~100%
3 flashes = Medium, 30~70%
2 flashes = Low, 0~30%
Voice Prompt Indicator
When you power on the headset, press and hold the Center Button and the (+) Button for more than 6 seconds until you hear three, high-toned beeps. Then you will hear voice prompt indicating the battery level. However, if you release the buttons as soon as the headset turns on, you will not hear the voice prompt of battery level indication.