I don't know.
I can guess though.
Perhaps it has something to do with amps.
It just occurred to me, if people are pumping 48V into this module, then 9V is totally OK.
All you have to do is take the bottom off, remove the battery sled for the AA and solder on a 9V clip.
Then the 9v battery sits in the space, and you just use gaffer's tape to hold it in place.
9V battery box, no problem. No extra anything needed.
I'll take a measurement now...of the resistor (?)