I’ve watched this thread and not posted much but I’ve just posted some of this info on another thread and it has a place on this one as well, because there is a case of horses for courses and you really need to know what's available and what will best suit your needs.
Idiot switches ( and this is not a derogatory term but a commonly accepted term to describe this type of set up ) are cheap, depending on how you intend to use them.
If you want a simple system that is only on while the motor is running, they are fine but they are not suited to being used while the motor is of because they require a fair bit of current to keep the solenoid powered.
Again this is not a problem with the motor running, but if you want some extra power while you camping, my SC40 and SC80 because of the way they work ( and is unlike any other DBS on the market ), you not only increase your auxiliary battery’s stored usable capacity by at least 50%, turning say an 80 Ampere/Hour ( A/H ) battery into a 120 A/H battery, but because it does this by using the surplus capacity of the cranking battery, you get a bigger battery at no extra cost. This actually works out cheaper than an idiot switch and you don’t have to remember when to operate it.
There are a number of other advantages, the obvious one is the automatic increase in stored capacity at no extra cost.
Because you are spreading the load over two batteries, you will help extend the operating life span of your auxiliary battery, another cost saving.
Again, because you are spreading the load over two batteries, so you will not need to take either battery down as low as you would have to do with any other set up, including an idiot switch set up and this means because the batteries weren’t as low when you start your drive, you will actually charge them in a much shorter drive time between free camping sites.
So, fitting the RIGHT Dual Battery Controller can actually work out much cheaper, immediately and in the long term, than fitting an idiot switch.
