Description: This product is Schumann wave 7.83HZ very low frequency generator, features high accuracy and stability. High stable frequency acquisition elements: high stability chip, precision correction capacitance, precision multi-loop adjustable resistor. High quality polymer batteries, with overcharged, overvoltage, overcurrent protection. There is almost no voltage ripple in the voltage supply. With work toggle switch, easy to use. Schumann wave can be applied to HIFI or sleep. Specification: Polymer battery capacity: 1400mah Time: charging current 250mA, 6 hours full of electricity Working current: 7mV Working time: 200 hours (full of electricity) Size: 7 x 5.5 x 1cm/2.76 x 2.17 x 0.39inch Package Includes: 1 Piece Schumann Wave Generator Note: Customer satisfaction is our primary concern. If the product is somehow cracked or broken during shipping, please feel free to contact us. We will try our best to give you a satisfactory solution.