Oner the Head Noise Cancelling Bluetooth Headphones with Built-in Rechargeable Lithium Battery Built-in Microphone for Cell Phone Bluetooth Version: CSR V2.1 Bluetooth chip backward compatible with V2.0, V1.2 and V1.1 standards, support A2DP, AVRCP, hands-free protocol Adopt dynamic circle speakers, no matter listen tenderness music or mental music makes your feeling into the music scene Adopt high definition voice calls(microphone) function, enjoy work and leisure High definition function: 2.4 GHZ Bluetooth Battery Capacity: Rechargeable Polymer Lithium Lon Battery 400mAh