Last night, I only placed the initial cleco's for the battery box. Today, I finished drilling the remaining rivet holes for mounting the box to the firewall. I then removed the box and deburred it and the firewall. Reattached.
Fabricated a box "floor" stiffener out of another piece of .025 stock. Since I built this box out of .025 instead of .032, I felt more comfortable adding some material. I also fabricated a battery lifting "strap" out of scrap stock. When the battery is down in the box, it is difficult to get a grip on it for removal. I just cut a strap out of stock and placed it under the battery before putting it in the box. I folded over the "ears" of it to prevent contact with the posts.
I then cut hinge stock to length for the 4 hinge sections that hold the top strap in place. Located and pilot-drilled holes for riveting.
Cut a length of stock to serve as the stock. Riveted one hinge halve to it, and located it and pilot drilled its mate to the firewall. Secured with cleco's. Bent down the strap in two places to serve as restraint to hold the battery in place as per plans. Riveted the other hinge half to the strap. Have not yet located or pilot drilled the other hinge half to the battery box.