The internal circuits of the TV run on 19VDC. The AC adapter provides 19VDC. Either there should be mention in the owner's manual about capability to run on lower DC voltage, or there is a DC/DC adapter to provide 19VDC to the TV from a 12VDC source.
BTW I have been researching this myself and found some Sony and Samsung TV and BluRay players that run straight 12V or 14V. But as a pause, what would happen to your device if there was a surge from hooking up to shore power or battery
charger? I'd rather have a DC/DC converter in between to take the blow, or at least keep an even regulated voltage to the devices.