I don't understand the question.
I understand that you want to watch TV off the battery. The way you do that is by installing a device called an "inverter". In simplest form, you can see these as 12v to 120V adapters that you see sold for cars. Modern TVs don't pull much power.
So the inverter needs to be installed in a position between the battery and the 120V circuit that powers the TV. For the RV case, the inverter also needs to be able to take AC power when you are plugged in.... So, as such, if you don't have electrical experience that leaves one of two options:
1) If you have a 20A 12V outlet in your trailer, you could rig up an inverter with an extension cord, just like you'd use in the car.
2) If you don't have an outlet and want to install an inverter, it's probably best to let someone who has RV electrical experience tell you how feasible this is.. It may have been an option for your trailer, which would make it easier to do.