Power! After cleaning up the battery box, today I temporarily mounted the box and the batteries, then cut the remaining fat wires and crimped on the terminals, adding heat shrink. I also fabricated copper bar for connecting the two batteries together. Then I had fun jumping the appropriate posts on the master and starter contactors, just to hear then engage. Of course I measured voltage at the appropriate places, including the power bus on the firewall. The voltage drop from the batteries to the power bus was only about a tenth of a volt, so it seems that those #2 awg wires are doing their thing pretty well. I still have to fabricate the battery hold down bracket, and clean up the box a bit.