His existing 12V receptacle is probably rated 10A, - good enough. It is possible that wires behind this receptacle are too thin to handle 3A-4A that an average small TV would draw, - odd but possible.
With inverter installed near batteries, if this is only for TV, pretty much any old piece of lamp cord will do.
It is also possible that replacing the wires in 12V receptacle with slightly beefier ones - if it really comes to this - will be easier than permanently wiring inverter near batteries.
He should begin with telling the TV wattage.
