Dual Battery, Perko Switch & Electronics Question

I currently have my 2 HB's and 1 Lowrance connected to an isolated battery that I charge between trips. I would like to link my isolated and my cranking battery via a Perko 1 - ALL - 2 - OFF switch.
I want this for 2 reasons:
#1. Should I have cranking battery problems, I can switch over to the other battery and start my motor.
#2. If my electronics drain my isolated battery during a trip, I can switch to it and let my alternator re-charge, then switch back to my cranking.

My question: When switching from Battery #1 to #2 Battery, as I understand, the switch passes through the "ALL" position. Does this create a 24 Volt surge in the "ALL" position, and if so, will it damage my Electronics? If anyone has this setup, lend me you knowledge, or how you setup something similar............Thanks

No it will not produce 24V - In the ALL position the batteries will be in parallel producing 12V but with the amperage of both batteries.

Handy when the cranking battery is pooped and electronics battery still has some life left.

Do not leave it in the ALL position when one battery is down and the other still has a good charge, as the discharged battery will drain the charged battery till the charges are equal.