I looked up the model you  posted,, (XM-18D)  but the wiring diagrams are slightly different.   From your pix above,, I see the 12 volt terminals as an output source.   Maybe for an external low voltage light???,, or extra 12 volt fan??
 
The unit needs to be plugged in  (L N stand for line and neutral  from home power outlet)  to provide the  120 volts needed to  power your ceramic heating bulbs.  
 This does not look like it would be an inverter that could/would provide 120 volt current from a  12 volt power source,,,, like a car battery.   Those terminals would be much larger, and heavy duty. 
I do own a power inverter that I only would use in emergency power outages.   The power cord cables that it has  to connect to battery are quite heavy gauge. 
I can search further if you could possibly  give me the more complete model number.   The XM-18D  probably covers more than one sub models. 
I understand electronic circuits.  
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,and 
