Parkside Team 20V Adapter and Undervoltage Protection Circuit

The budget Parkside Team 20V batteries contain very good battery cells, so I decided to use them for some mobile applications (soldering iron, power supply, etc.) and designed this adapter to connect. Only drawback I can see: the cells do not contain an undervoltage protection circuit, so I added one here as well.

The adapter itself has 4 holes for M3 screws and nuts to mount a case on top of it.

For the contact, I used PCB tabs ("Flachstecker") and heated them with a soldering iron to melt them down a bit. I also fixed them with some hot glue. The wires go through two holes also on the top side.

OpenSCAD file is attached - feel free to modify them for your own needs!

CAUTION!
It is dangerous to deep discharge Li-Ion batteries, as in the worst case they will not only be destroyed, but can burn/explode when re-charging after a deep discharge!

That's why I also added a simple undervoltage protection circuit with some spare parts I had lying around. See the schematic and pictures attached. Only a few common parts are used: an LM358 as comparator with hysteresis and a MOSFET to cut off the voltage. The potentiometer is set at 15.3 volts to protect the batteries (a little leeway for safety since the cells are not symmetrical).

Julian Ilett has disassembled and analyzed the batteries so you know what you are getting:
https://www.youtube.com/watch?v=CN0q4wZBnBo
(There appears to be an overcurrent fuse in the battery).