Originally Posted by HowieE
Do not get sold on a so called trailer battery Isolator. There is a diode in all of them and the voltage drop across a diode is .7 of a volt thus you are at a loss before you start, but Camper World has to make a buck some how.
This used to be true but isn't, necessarily, any more, though there are still cheap diode isolators out there. Avoid them.
There are two other kinds.
One uses a MOSFET or similar device to do the switching. These are semiconductors, but don't have an NP junction like a diode. No junction, no diode drop. The problem with them is that they are expensive and are easily damaged by overcurrent, and the ones that are big enough to handle a short long enough for the fuse to blow are really expensive.
The other kind uses a big relay, operated by logic of varying sophistication. The simplest of these close when the voltage goes up above 13.5 or so and open when it goes below 12.7. Others incorporate time delays to minimize nuisance cycling.