The quickest and most likely the safest way is to use a small DC to AC Inverter.
A inverter takes 12V DC battery and converts it to 120V AC power.
Less safe (and hence dangerous to the device) follow information below..
IF your device uses a separate "power supply" which plugs into 120V wall outlet AND it has a plug in to the device you MIGHT, be able to connect the device to a 12V DC source directly provided it is marked 12V DC..
Your devices power supply might be 12V, if so, it might be possible to rig up a power cord with a cig light plug on one end and the matching DC plug to the device.
If your device is marked 5V DC, then you might be able to use a 12V to 5V USB charger as a way to connect your device.
This however can damage your device IF you miswire the polarity OR the device is extremely sensitive to overvoltage (12V computer type items tend to MEAN 12V as in 11.9V-12.1V and not 13V-15V you get from an automobile battery system)..
If you are not adventurous or willing to potentially sacrifice your device then going the inverter route may be best for you.