Finished installing the battery box. In the never-ending saga of its design, I had to modify the hold-down bracket and the jumper between the two batteries to enable the rear hold down bolt access. Later I placed diodes in the appropriate spots on the ground and master contactors. Then tested both and they work just fine.
Also, I made wooden blocks to the approximate size of the various Garmin components that need attachment to the airframe, such as the AHARS, ARINC, etc. I'll use these to mock up positioning of the actual units.