New TV usually have external power supply, around the 19V Dc range or higher , that are similar to laptop power, what i did was to buy a small Dc to Dc converter from china and that works great for me. The converter will use the 12v Dc that is in the RV and convert to your desired Dc voltage for your TV.

did you put an dc amp meter on the wire comming from the battery to the 60 amp breaker to see if the amperage was close to the 60 amp breaker value