I cut away the front of the battery compartment so the battery will slide all the way out the nose. I cut a flat piece of thin plywood to form a shelf. I Gorilla Glued a length of square cross-section basswood to the end, to form a brace for the … wall at the end.

Then I glued a slightly thicker piece of plywood to the brace, at 90 degrees to the shelf. The bottom shelf will be glued into the bottom of the original battery compartment.