Perhaps this was already obvious to others, but I gently “unscrewed” the yellow footpads on my OP-Z (just with my fingers), found the back of the case opens easily, and inside I found:
User-replaceable battery, as promised
Under the battery some graphics that any space geek will recognize <3
The default module cartridge seems to be intended as a iphone holder? Looks like you can snap out the legs and attach them to the outside (haven’t dared do this myself yet, anyone else?)
I found knobs on thingiverse so I will model a hole into it to attach it to a keychain when I’ve printed it so I have my opener always with me and can store the phone holder inside the case.
Not sure if this has been mentioned anywhere else already. But for anyone who has really stubborn yellow screws on the back plate. Try using the sticky part of some packaging tape pressed against the top of the screw with your thumb to get good grip. This was the only solution I found to unscrew my backplate without destroying the screws.
Once you get the plate off you can adjust the tension on the 4 screws by loosening/tightening the tiny black screws on the underside of each one.