I started with about 11, then decided I would go and find power armors to try and find an X01 set.
This involved going to known locations while wearing power armor, and grabbing pieces off the frame, then I'd come back without power armor, stick in a fusion core and grab the frame. I'd bring the frame back to my settlement, park it and remove the core.
Rinse and repeat. I have a [censored] ton of power armor now, mostly t45, t51 and t60's, along with about 20 armor frames.
Everytime I grab a new power armor frame it would pop in a brand new 100% full core into the frame. When I'd remove it they were about 89-99% full.
Somehow during this entire process I've gone from having 11 full fusion cores, to 17 full fusion cores and 24 used fusion cores with anywhere from 89-99% charge in them.
Did I discover some kind of bug? because I sure as hell haven't been picking up this many cores all over the place and none of the armor or frames that I grabbed had cores in them.