I've received Carl's schematic for dual batteries and he's reinforced to me via emails the importance of being able to get that power to the critical places with no to minimal pilot action. I absolutely agree with the previous post about making your system too complex. That in itself adds a degree of increased risk.
Here's my thinking. I'll have two batteries and one alt. If I have an alt failure, I would be notified of that by the Dynon EMS. If I confirm/agree with the EMS of an alt failure, all I have to do is flip the two switchs to get power from BOTH batteries directly to the avionics and turn off the master switch. Power from the batteries will be direct to the avionics with the only connections being 1. At the battery 2. The relay (power in and power out) 3. The avionics buss connection.
With the Dynon's back up battery and the built in G5 battery along with the two full size batteries up front, I feel this would give me best I can figure an absolute minimum of like 90 minutes to get back to VFR or below the clouds.
Discussion: Carl's stresses the importance of getting the power to the necessary equipment. I agree. That includes battery grounds. Each of my batteries will be grounded side by side to the airframe/engine block.
A thought on the relays that will be the only thing inline between the batt power and avionics buss. The connection for power in and power out of each relay from each battery to the buss. There is of course the wires running into the cockpit for the switch and switch to ground that could fail too.... as well as the switch itself. Here again, There is ANOTHER switch going through the other relay to provide power from the other battery directly to the buss. OK..... What are the odds of first an alt failure followed by a second failure of a relay/switch/wiring connection at the same time and if that WERE to happen, there is the second battery with the exact same setup to get power from that OTHER battery to the buss? Admittedly I'm just learning all this stuff and am speaking from probably the most inexperienced point of view on VAF.
Reviewing my own schematic, I see there's a single point of failure at the 25 amp pull breaker. If that did happened it would only make sense to turn off both "direct to" relay switches again and go back to the battery only side of master to get power to the avionics buss. I wonder if it would make sense to leave the batt side of master on from the beginning of the alt failure and turn on the two "direct" source switches. Of course this last would add the importance of sheding all unnecessary loads from the main. The advantage is now there are THREE ways power is getting from the batteries to the avionics buss.
Any thoughts are appreciated.