For mp3 players and other devices that get their power through usb plug your device39s usb cable in and charge from almost any vehicle39s 12 volt accessory outlet with this low profile micro form factor powerjolt works in your vehicle39s 12 volt power outlet charge 2 usb devices at the same time smartfuse circuit breaker protection means no fuses to replace super compact form factor 5 watts per port 5 volts 1 amp