I want to put a disconnect switch on the RV battery side, so that there are no trickle discharges over the winter, etc. I bought such a switch, looks really simple, but the instructions say to put it on the negative battery post. I can't see the logic for that, at least not for what I want to use it for. I there any reason why I would not put the disconnect switch on the positive side?

Either side will work. I had one, that disconnected the entire electrical system from the battery, however I thought it was a bit flimsy to carry the starter and heavy charging load. My PO had it on the positive side of the system. I changed it to only disconnect the 10 milliamp load from the dash leaving direct contact for starting and charging, but no amp draw unless starting or the ignition was on. BTW I believe the negative side disconnect is better, because if it is an open spade type switch and you happen to touch it with a tool and ground at the same time there is no short! Safety issue!! If you do what I did you will have to do it on the positive side.

Good stuff, thanks.

The BMS used on lithium batteries all turn the battery connection on and off on the negative post.

I have mine on the negative because when you turn the knob to disconnect the cable comes off the battery. If I had it on the positive, I would stand a chance of my watch or rings ( If I wore either ) of shorting out because its very tight in the battery compartment and I might get between the hot post and the battery compartment. But I would think depending on how your disconnect is made, hot or ground would accomplish the same task.

My disconnect is a T handle Flaming River that Richard built into the custom cover for the Optima. It's mounted to the positive side of the battery. I did learn that when I'm using wrenches on the terminals of the disconnect that I MUST first take the battery terminal off. I don't know why Richard put it on the positive side but he builds race cars from the ground up so I'm not questioning him.