I bought two devices. Both have an audibly positive effect on music playback with the devices now supplied with clean power (rpi/WiiM/Dac). The first device is flawless. The batteries of the second device are weak. The batteries are empty after approx. 3 hours. Two green LEDs still light up, then the device switches off. On the first device, the batteries last for at least 5 hours without any problems until all LEDs go out.