The headphones have a built-in rechargeable battery. A complete charging cycle takes approx. 3 hours. The headphones provide 1.5 hours of playback time with a charging time of approx. 10 minutes. Before using the headphones for the first time, charge the rechargeable battery for a complete charging cycle without interruption.
When the headphones are being charged, the LED display lights up (> Overview of the LED display). When the battery charge drops to a critical level, a voice prompt asks you to recharge the headphones (“Recharge headset”).
Sennheiser recommends using the supplied USB cable and a compatible standard USB power supply for charging the headphones.
While the headphones are being charged, you can still listen to music or make phone calls. In this case, however, the charging time may be longer.