This is my first time at using two batteries so I like to understand how others have done it so I can learn more.
Mine too, and I also spent time learning/understanding how to make a setup I was happy with.
I started with a project that was 90%/90%, included dual batt, and dual alternators, but no wiring or schematic.
After a lot of studying Nuckols, and talking to local aviation guys, and more than a little design/re-design work, what I came up with is -----
Main batt (Odyssey 925) is powered directly from main alt---60a. Aux batt (Odyssey 680) is powered directly from aux alt---8a. Both systems have the normal master, field switches, and regulator setup.
The items I considered to be required for normal flight------Dual GRTs, radio, xpndr, intercom, and electronic ign are all powered directly from a buss fed from the aux power circuitry.
Everything else in the plane is powered from the main buss, and the main buss feeds to the aux through a high current Schottky diode.
In addition, I have a battery cross tie contactor that I installed to facilitate starting, if the main batt gets weak. An un-intended side effect of this is that the Aux alt is able to also charge the main batt, when the batteries are tied together.
In ground testing, all seems to work well so far. I can light up the panel from either master, and switch to the other buss with no drop out of the EFIS, or radio stack. As I havent started the engine yet, the charging side of things is yet to be proven, but it is sound in theory, so all should be fine there also.
For those who noticed that the aux buss doesnt power things like boost pump, pitot heat, flaps, lighting, autopilot, and etc, correct. I designed the system so that in the event of a main elect failure it will allow me to safely fly for an hour or two if needed, until I could find a place to land, and fix the problem.
As Stein would say, my $.02.
Hope this feeds the knowledge hunger a bit.
Good luck.