I mounted my battery in the UCD the following way:

1) I cut a large hole in the balsa sheeting on the fuse bottom, almost the whole width of the fuse and maybe 4 inches long just ahead of the bulkhead in the middle of the fuse.

2) Snip the battery wire and solder in a 12" or so extension.

3) With the plane inverted drop the battery in the hole so it rests on the top of the fuse and is against the bulkhead. CA a piece of balsa sheeting to trap it to the top of the fuse. CA a balsa stick to stop it from sliding forward.

4) CA the sheeting back on the fuse bottom

5) Cover with monokote trim sheet or monokote.

Took about 30 min. I have no access to the battery but I don't need it. I mount most batteries in the back of the fuse, saves tons of lead.

Just another option.