Smartphone Speaker. Simply lay your smartphone or Mp3 player on the speaker to amplify sound no matter where you are without wires or pairing, as it interacts with the speaker on your device so you get instant magnification. Up to 10 hours play time before you need to recharge the DC5V battery with the included USB cable, or using the 3.5 mm port (3.5mm cable not included). 3.7V 850mAh lithium ion battery, 4 O/3W speaker. This small and lightweight speaker is compatible with most smart phones and MP3 players with external speakers.