Main Breaker versus Battery Disconnect

The main breaker is for the 120 volt system, a battery disconnect switch is for the 12 volt system. If you have one of those switches that go on a battery post, replace it with a switch that can be mounted outside the battery box. Turn off the switch whenever the trailer is not in use because there are some small loads that will drain the battery. I use a Blue Sea on-off switch, don't buy the cheap ones with the red key.