I don't think thats actually legit. It's the property itself that needs the TV license and each individual room is classed as a seperate residence.
TV licensing came around at university once and stuck up huge posters everywhere telling people about how they're not covered etc... and they'll be checking. I don't recall anybody ever coming around or acting suspicous outside with a van though.

When I was off campus living in a flat some guy knocked on my door saying he was from TV licensing and if I had a TV. I said no and he said oh okay and left

A battery powered TV however is covered under your home one though. Not sure what they'll say to a inverter and a huge battery though