I've had a look at the gaps that you've mentioned and I think it may be due to the slicer (or settings) that you're using. The model itself checks out (no naked edges, watertight etc) but the area that you've highlighted is only 2 layers thick in order to maximise space for the battery. When I slice the model here using Makerware at 0.2mm layer highlight everything looks and prints fine with no gaps. If the gaps are an issue that can't be fixed in the slicer then the other option is to increase the wall thickness in that area by modifying the SCAD script, specifically the fillet radius which is line 143 from "rounded_cube_2(bat_c, 1, "yz")" to "rounded_cube_2(bat_c, 2, "yz")". I can upload a version of the STL with this change if that would help.