My guess is that you meant that the appliance takes 120VAC
The problem is that a car battery puts out 12VDC
Because there is not only a different voltage, but also you different form of current (needs alternating current, gets direct current), you need what is called an inverter. It takes DC and turns it into AV. They are very common and most are made for that specific purpose and go from 12VDC to 120VAC @ 60Hz.
Most automotive inverters plug into a cigarette lighter and have standard 120V 60Hz wall plugs for output. You can then plug in any standard home appliance or such into the inverter.
Most appliances that use AC input (like 9VAC or 12VAC) will *usually* work with a DC input voltage.
The reason is that *usually* the AC gets rectified into DC inside the appliance anyways.
You could try feeding it 12V DC and see if it works.
It shouldn't hurt anything,and it doesn't matter which wire is + or -,because the rectifier inside will "fix" the polarity for you.
This is assuming a full-wave bridge rectifier... if it's just a simple diode or half wave, it just won't work one way, swap the power wires around and try again, it should work.
95% of the time DC will work just fine, but I make no guarantees.