I just finished a new battery box for my Fly Baby. Actually TWO battery
boxes, after the first one (made of oak) got laughed out of my EAA chapter.

(Hey, I do a bit of non-aviation carpentry. I *love* working with oak!)

FWIW, the poplar one weighed 1.25 pounds. The nearly-identical oak one
weighed a half-pound more... a 40% weight penalty.

I'd have thought you'd use spruce, it's even more poplar... :-)

Ed Wischmeyer