Discussed operation of the TCW backup battery with TCW. Confirmed that the "normal" operation will run the main battery down to ~11V which might be 10 or 20% capacity remaining and then switch to the TCW backup. Also the main battery will try to charge the backup battery until the main battery reaches ~ 11V.
If I want to run lights, fuel pump, flaps, etc on the main battery and run the avionics on the backup battery as soon as the alternator fails, then I will need to have an "avionics" master to disconnect avionics from the main bus and to remove power from the TCW sense/charge line. This allows me to decide when I will use each power source and whether the avionics will run from the main or backup battery.
I updated the wiring spreadsheet with several different options and decided I wanted to leave the trim and autopilot power connected to the main bus and the remaining avionics connected to the TCW backup battery. A single Otto K1 switch will work as the avionics master. I also confirmed a single TCW backup battery would be enough for my needs.
I created more panel switch labels. I created a 1:1 scale footprint for the ground tabs and TCW battery backup. Tried a few different switch layouts on the panel and started looking at where to mount all the avionics boxes.