Battery cut off and selection switch install

Just installed a marine style battery switch. I like to be able to use one battery at a time. That way I know when I am on the second or what I call my reserve. That way if I happen to leave something on by accident and come back at the end of the day or wake up in the morning with a dead battery I just switch to number 2. That is also why I use two 12 volt instead of two 6 volts. This has worked well in previous RVs and boats. Just some food for thought.
The switch has 4 positions  off, battery 1, battery 2, and both 1,2 for charging.