Your plan is not only economically foolish (Penny-wise and Pound foolish) It is very questionable ethically.
While trailers do not often come unhitched during travel , it does happen. And if that should happen to you you owe it to the people in the car behind you and the others around you to have that very important safety feature working.
It is Legal Negligence. I know if I was the Attorney for the injured parties I'd not only find this conversation for evidence but I'd OWN you and you'd be lucky to escape criminal charges for Criminal Negligence resulting in Bodily Injury or Death.
Get a Battery. Period.
