That's actually how I found this thread, your videos on the subject! It's nice to see someone willing to mess around with one of these beasts. I may end up following your line of thought and attempt to replace the cells in my battery as well, as while mine was brand new, sitting in a box for...
You would be absolutely correct in that it was designed with "hot swapping" in mind!
Here's the relevant page from the manual, describing gba cart functionality.
I picked up one of these new in box years ago. Took me almost 3 years after that to track down the damn controller. Wish I had...