The battery disconnect switch has made a huge difference in stopping the passive drain from our batteries. I just want to caution anyone thinking about installing a disconnect switch to investigate carefully the range of switches that are available and the manner of connection to your battery.
The ones shown above are external to the battery and look pretty much like the wall switches installed in many RVs. That's fine if you can do it that way. There are other types which connect directly to the battery terminal and may be better suited to being attached within the typical RV battery compartment.
The basic types of 12V battery terminals are the "SAE post" type which consists of a post to which the battery cable is clamped, and the "General Motors type" also known as "side-post battery terminals" which have threaded fittings on the side of the battery.
The complication on some RVs, like ours, is that they use an SAE post battery terminal in combination with threaded fittings for some or all of the battery cables. For this reason, we ended up needing a side-mount (GM type) battery disconnect switch that actually fit on the threaded fitting on the TOP of the battery.
The type I ended up using that has worked very well is this:
WirthCo 20128 Battery Doctor Battery Disconnect for Side Terminal
https://www.amazon.com/dp/B000CQFWLY..._Qh94ybKQXYNZS
I first tried using this screw-on and -off type which many people have posted on this forum. I had tremendous difficulty with this because of the tight battery compartment on the RV. The amount of torque exerted by the battery cables (because they are bent and trying to unbend themselves) caused the two parts of the switch (basically the top and the bottom...) to twist apart. This resulted in arcing and sparking when opening or closing the screw switch. Also I could never be sure it would stay off because of the twisted components essentially being in constant motion in a moving vehicle (say 1/16" clearance between the two components at best).
Docooler Battery Terminal Link Switch Quick Cut-off Disconnect Car Truck Auto Vehicle Parts (Battery switch 1)
https://www.amazon.com/dp/B00GJMDTH4..._Pj94ybW0AFXM1
I even tried super-gluing the two components together but could not get them to stay attached. The torque of the battery wires quickly broke the glue. I ended up asking for a refund, which the Amazon seller in China gave me after a couple of email exchanges and a nudge from Amazon.