The brakes will work, (assuming you have 12V feed from the truck) but the emergency disconnect brakes WILL NOT. I believe it is technically illegal in most places to tow without the battery (?).
That being said, in my case, I sometimes have a case of CRS (Can't Remember S#!t) and forget to bring the battery when I go to pick up the trailer from storage. So I risk it and tow the 5 miles home without it.
-2018 Greyhawk 29MV
-1997 Jeep Wrangler YJ (Toad)
-2015 Jeep Grand Cherokee Limited (Soon to be Toad)
-2014 Jay Flight 28BHBE & Ram 2500 6.4L CC 4x4 (sold)