I disagree with some of the posts on here about budgeting for a battery. Just because a person has a budget doesn't necessarily mean they can't afford nicer things in life. It just means that they are aware of where they spend their money. I also disagree with the statement that trailer ownership is expensive. I would say my total cost for maintenance is less than $50 a year for a couple of tubes of caulk and maybe some bearing grease.
To answer the question about whether you need a battery. That has already been fairly well covered, but in general:
Some converter/chargers require a battery, some do not.
You will need a battery to operate the refrigerator on LP while driving down the road.
You will need a battery to operate the trailer brakes in the event that the trailer becomes disconnected from the tow vehicle.
If you are always going to rent hookup sites then any inexpensive 12 volt automotive battery will work. In fact as noted previously you can probably get by just fine with a $30 lawn tractor battery from Walmart to operate the brakes if the trailer becomes disconnected.
In fact if your tow vehicle battery is getting old and tired you can buy a new battery and put the existing battery into the trailer. You'll lose your nine dollar core charge, but you'll also gain a trailer battery for nine dollars.
