Bergmann Technik EP-355 Stüdyo Kulaklık ∙ Bluetooth Version: V4.2 Working Distance Range:10m Battery Specifications:3.7V, 300mAh Built-in rechargeable lithium battery Charging Voltage: DC4.2-5.5V ∙ Charging Time: about 2h. Talking/Music time:about 10 hours Driver:2 x 40mm lmpedance: 32Ω ±3Ω ∙ Frequency: 20Hz-20,000Hz