Hello Kas,
your battery discharger is exactly the type of projects I bought my Arduino for, but I'm afraid I'm not fit enough yet to get it done by the plan and the photos, so I would very much appreciate if you could answer me some questions:
-what is the green (quite big) part on your photos? I assume it is R2? You talk about a shunt resistor in your text. Is this the part and what are the specifications that I have to search for when I would like to order it?
-I would like to build your AdaFruit Shield version. In the photo I saw that you use a different IC there. Is it LM358N? Is it used the same way as the LM324?
-Do you have some more photos of the AdaFruid Shield version? Is it Version 2 already?
-how is the jumper for different voltages wired?
Thanks in advance. I'm looking forward to measure the capacity of my rechargeable battery collection (mainly AA and AAA-types)