The information on their sight is a little confusing.
The rundown of how that system works is:
With the switch in the DUAL ON position the batteries are tied together when the switch is ON, this means they will both charge while the engine is running, and depending if the "switched ON source" is live during cranking (most are) its starting off of both batteries. (Don't care what they say on the site, without a latching relay in my diagram or like said before a oil pressure switch both batteries are being used to crank because the isolation relay is energized while cranking)
With the switch in the EMERGENCY ON position the isolation relay is energized all the time, no matter of key position
If the key is in the accessory position and the DUAL ON switch selected, the isolation relay is not energized so the aux batt is not being used by the Jeep's electrical system.
I said all that to say all this,
I don't care for this system....it works great for its intended purpose, but if you leave the key on, you've drained both batteries.
I prefer a system that will only connect the batteries together to charge while the engine is running. This eliminates almost all possibility of killing BOTH batteries.
There are products on the market that will totally isolate batteries, and only charges both when the alternator outputs voltage. This is the simplest and easiest way to go, but the isolators are expensive and the same outcome can be accomplished by some simple wiring and parts that are already going to be used.
Sent from my phone where correct grammar is difficult.