The BT-168D battery tester can measure 1.5V AA and AAA batteries, 9V batteries, and 3V button cell batteries. However, it has a dimensional limitation and cannot measure 3.7V 18650 Li-Ion batteries by a few millimeters. Furthermore, to measure the batteries, you have to hold them by hand between the two terminals, which is awkward.
This modification solves both problems: 3.7V 18650 batteries can now be measured, and the batteries can be measured by placing the tester on the table with the battery resting on the table itself, since the thickness of the lower casing has been reduced and the terminals are positioned much lower.
I made the slide in two parts to glue them together later. I did this to avoid using supports in the slicer, as supports make the slide section that fits into the groove look much worse.
The upper piece with the display is original and doesn't need to be replaced; only the lower piece, which is screwed in, needs to be manufactured, and the sliding mechanism replaced. Of course, the terminals need to be reattached.