Built-in lithium battery, equipped with a micro-USB cable, can charge the battery. The four lamp battery indicator light will always flash during charging, with a low power consumption of 5V and 0.08A. The sine wave is generated by a programmable smart chip and operates at 7.83Hz. Waveform, frequency, and power can be set according to your needs (fixed by default). This for Schumann wave generator has higher frequency accuracy and stability consistency. Colour:White Material:plastic Package Contents: 8 x Schumann Wave Generator Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.