It does what it says on the tin: it holds in your batteries! I got this meter second-hand without the battery cover. The dimensions could need a bit more refinement, because my calipers are way more accurate than my printer. If you can use the STEP file to make any corrections, please remix and repost with attribution.

Print with the flat side down and enable supports, which should only be needed for the two ears at the top, and the counter-bored screw hole.

The meter takes an M3-0.5 screw for the battery cover. I used an 8mm long button-head with a lockwasher. As you can see in the last picture, it protrudes a bit, but not past the "feet" at the corners of the meter. If you omit the lockwasher, it screw head sits just about flush with the surface. If you omit the lockwasher, a 4mm long screw might work.