A case with a tapered press fit cover and screw mounting for a xl6009 dc-dc boost converter board. 

Either M3 or #4-40 will self tap into the mounting holes for the board.  The lid is a tapered press fit.  
I didn't include mechanical strain relief, there are narrow slots to allow the in and out wire pairs to pass.  I used a dab of hot glue on the inside as my strain relief, you could also use knots in the wire, or a zip tie. 

There are some different variations of this board, so I designed this case to fit the larger of the two I've seen. The small boards still fit, but only one screw can be used, which works fine anyway.  See internal dimensions and hole spacing here: