The battery on the ND looks “exposed” and really needed a cover, so today I cut down a piece of acrylic sheet (3mm) that was matt on one side and high gloss on the other. I thought matt finish would look better.
The attached photo is Experiment 3 (Experiment 1 was cardboard, Experiment 2 was hardboard). The cardboard fixing point looked like an ear and I was concerned about stress, so made the hardboard one and the acrylic one with a long slant around the fixing hole.
Unfortunately, the blade on my jigsaw did not have the correct number of teeth for cutting acrylic, so the edging is not as I would like. I had to use a couple of plastic sleeve nuts as I had no stainless ones in my toolbox. There is a scratch on the cover in the picture - note this is still Experimental. The left hole was 1mm out so is also slightly bigger than planned. Final version will have polished edges and a sharper cut.
This mounts on the existing battery restraining bolts and no new fixings are required.
Hope it gives you some ideas of your own!
Experiment 2 . . . .
Experiment 3 . . . .