Bit of an odd question, but why bother?
Max mAh for 3 x AAA is 3 x 1100 mAh = 3300 mAh. For an 18650 battery it’s between 2400 – 3000 mAh, usually. AAA rechargeable are nominally 1.2v and an 18650 is nominally 3.7v.
So it seems like energy stored and voltage would be about the same?
I may be missing something, but would you see any real benefit? Perhaps someone may be able to explain this to me!