I don't have too much familiarity with RV's, my experience lies with cargo/horse/stock/flatbed trailers. That may be the case with all RV's. But again, personally, I would keep the system separate. I know it is unlikely that you would drain a couple batteries if you left the lights on and your charge circuit wasn't operating. I just keep thinking about that "what if" situation. If your lights were left on too long without a hot circuit charging from the tow vehicle you wouldn't have any juice to send to the brakes if your Break Away switch was tripped.

 

On a camper yes, the coach batteries dump to the brakes when the switch it pulled. On utility trailers there is a smaller gel cell battery that will do this. On surge brake trailers, the pin mechanically pushes fluid into the brakes and lockes them out for bleeding down.

but you CAN isolate the coach batteries from the brakes. the 20a charge line will still run to the battery charger (its a small 2a charger usually, not an alternator direct connect) and the small breakaway battery has a tiny trickle charger in the harness.

 

I don't know of many RV manufacturers that wire that break away switch into a separate battery...

However it is possible if someone wanted to rewire it.

On bleed off...the LP detector (propane) that ALL RV's are REQUIRED to have DOES indeed provide sufficient draw to run a battery down in less than a weeks time.

I routinely disconnect one of my battery leads when I store my camper due to the draw from the LP detector...easier than pulling the fuse I guess at the breaker box inside.

Also it is important to have ANY battery connected to the RV or trailer when towing to provide 12V power in the event that the trailer does separate from the TV...too many folks I've talked to in campgrounds simply do NOT understand nor make that connection...dangerous to say the least...

Anything is possible with combinations of running down a battery or getting a dead cell, etc...trying to cover all possibilities would be futile IMO...simply understanding HOW your RV operates would be a good start IMO...which I've found many sadly don't even understand the basics...

Some people don't even know that some brands of TV's require that you install a separate RELAY in the power distribution box to provide CHARGING current to the trailer battery thru the 7 pin connector...without that relay...you aren't charging the trailer battery while towing either...I don't believe this is true for Fords...but there may be some of ours like that too...not 100% sure though...

Know YOUR equipment is the best advice...

And YES to the OP...you NEED a 12V source ON the trailer to operate the electric brakes in a break away situation...

Good luck,
joe.