Originally Posted by Phoenix
A battery isolator switch completely disconnects the battery (or batteries) from everything in your Airstream (the same as removing them). This keeps them from overcharging and boiling dry, and from going dead in storage (from parasitic drains, like the propane detector or subwoofer).
With the switch turned OFF, batteries can last for extended periods in storage without going dead. Most AGM batteries will last a year or more, and still retain a useable charge.
That is not what I would call a battery isolator switch and not what the OP posted a picture of. He posted a picture of an automatic isolation switch to separate a starter battery and a deep-cycle battery when they are being used and connect them while being charged.
I would call what you described a battery disconnect switch.