1The LED power indicator clearly indicates the working hours, avoiding the worry of insufficient power. 2Compact and lightweight design, easy to carry, easily fit into your pocket. 3Heavy metal tones, builtin distortion adjustment knob, volume adjustment knob. 4Use the earphone cable to connect the MP3 audio device and the amplifier, and then plug the amplifier into the loudspeaker. 5Built-in polymer lithium battery 500mAh, charging time is only about 1~2 hours.