Originally Posted by apachewolf
I always use a master disconnect on the NEGATIVE side, that way all power is disconnected, no guessing about "phantom" loads draining the battery when you think it is disconnected. In car service you always disconnect the negative first to ensure total disconnect.
That is not
why you disconnect the negative cable first. You disconnect the negative cable first because disconnecting the positive cable first runs the risk of shorting your wrench to ground.
As for a battery disconnect, disconnecting either the negative or positive makes absolutely no difference. Once the circuit is interrupted, no current will flow.
The reason why there are phantom loads in RVs even when the battery disconnect is off is due to those loads being attached to the battery before the disconnect - as they need power all the time (and should not be "disconnected").