3D-printable battery covers and battery packs?

[emece67]

Surely somebody can help this absolute newbie on 3D printing.

When uploading the .stl files to shapeways.com, they ask me the length units used in the models (mm, inches, m). What must I select?

I suspect they are mm (I've opened the .stl file with a text editor and the magnitude of the numbers there seems mm to be a reasonable unit), but cannot be sure.

Thanks to all.

Edit: apparently, shapeways has offices at both sides of the Atlantic, three in the States and one in Eindhoven (Netherlands). Thus I expect the shipping costs to be reasonable at both sides.