Running accessories from either main or aux battery.

[the evil twin]

Now that I've installed a my AUX battery and wired up a fuse box inside the car, I'm about to start re-routing all my accessories (stereo, USB chargers, internal lights, 12v chargers, fridge, power windows and so on..) I started thinking.. What if my AUX battery dies and I need to go back to using the main for a little while??

I've thought about getting a few of the switches attached below and wiring up each accessory to both AUX and main, but that'll mean switches everywhere... on the upside each accessory can be independently controlled.
Second option would be to have a single one of these that lets me switch all accessories at once to either AUX or main battery.

Curious what others have done?

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What battery manager do you have between the Cranker and Aux?

If it is a VSR (that is a Redarc or whatever) just hook the "Aux or Main" switch to the VSR override terminal.
Switch Off = Aux
Switch On = Cranker