The reason for the 11.8 VDC battery
voltage is that I tested
the TV at the rear of the 5th wheel trailer I live in. The distribution
panel is in the front about 30 feet from the outlet. So, under no
load the voltage is about 13.2 VDC (float voltage of the converter),
but under the 2 amps the TV draws at low volume there is a
significant voltage drop because of the light
gauge of wire the
manufacturer used and the distance from the fuse panel.
The wall power supply is marked 14 VDC 3A. The measured output
of the switching external power supply was 14.6V DC with no load.
It was surprising that the TV operated satisfactorily at the low
11.8V DC voltage.
Good luck finding your TV.