If you need USB power and you have access to a car or a car cigarette lighter plug that has power, this is precisely what you need.
I really liked how this example appears to be thumbing its nose at copyrights of Apple and Microsoft XboX.
Some models are tolerant of input voltages from 12-24 volts some are not.
Some models advertise what level of current they supply, 1 Amp is common.
Input 12V-24 DC output 5V DC 500-2100mA
these devices only supply power to the USB device not data, this device will not allow you to ‘download a car’ or some other wizardry.
Cost: about $10 for electronics and car accessory shops. Cheaper models may be available with lower output current.
Wizardry sold separately*