Orion TR Isolated 30amp charging lithium from lithium

Hi. I have an Orion TR 30amp isolated DC to DC charger on my boat. My cranking battery is a Dakota Lithium DL+ 135AH and I am wanting to charge a 100AH lithium battery with the Orion while keeping it isolated. The motor is a Mercury V10 400HP that has a 150amp alternator.

I’m having difficulty figuring out what to use for engine shutdown detection with this setup. What do you recommend?

Thanks!