Looks like I need to learn alot more first? I have only been doing this with no prior experience for a couple of months..
What the exact use of this sketch is to have a secondary battery in my van for powering other things whilst parked up with the engine off. Obviously then I want this battery isolated so as not to drain the main battery, then when the engine is started and the alternator is working, to switch a relay to reconnect the secondary battery for charging..