Replacement Battery Headphone, Bluetooth Wireless Headset, Half-in-ear Earphone with Earhook, Dual Detachable Battery, Smart Voice Prompt, Compatible with Digital Equipment with Bluetooth V4.1 Dual detachable battery:Mini size, light weight and flexible .The package comes with a spare 60 mAh battery as backup. No need to worry about POWER OFF when you are outside Stable signal transmission with CSR chip: You can connect your device (eg.cellphone) with the headphone within 10 meters. Also, you can connect two device at a time Noise cancellation: Half-in-ear design with a earhook can bring you a wonderful surrounding to enjoy beautiful music even in the noisy street Simple to Use -- With voice guidance, control all functions of your music (volume,pause, song selection) and Call ,Answer, Redial