Wall

Kesa Tiho
Same thing with mine, my guess is that you can also use it to store the batteries for led lights youd place into the ship itself.
If @Steven Van Dyck is wrong then it's just lost to time.

Steven Van Dyck
Check the timeline of this kit, it goes back to 1978. They even sold an engine apart from the kit then, but now that's out of fashion or even considered unsafe to have kids tinker around with 4 batteries in selfmade circuits that can get waterlogged and they leave out all electric components. You would have to look at that original kit to have them, I don't think they are that rare to find.

Check step 3 of the manual for the engine nstallation. scalemates.com/products/img/2/0/1/121201-91-instructions.pdf