Perko battery selector switch

[awthacker]

I thought I understood how this device works, but have gotten pretty confused - and I'm having trouble getting my electrical system working properly.

On the back, the lugs are "1", "2" and "common". My understanding was to tie the +12V lead from battery 1 to "1", +12V lead from battery 2 to "2" and everything from the boat (+12V to bus bar under helm, +12V to engine) to "common" (middle lug - currently only has engine lead connected in picture).

I guess what this offers is that I can run off battery 1 all trip, then switch to battery 2 if needed. Next trip, run battery 2 with 1 as the backup. Using the switch this way would offer one battery as backup reserve each trip. I don't think I would ever use the "Both" selection on the dial.

This seems different from alot of wiring setups I've seen, where one battery is the "house" and one is the "starting". Is there an advantage to this system?

What is the best way to use the switch?

Thanks,

Aaron