Oooh, that's a nice device. However, I don't think you really want to _fully_ charge your internal battery from AA's. The way I understand Li-Ion batteries, they charge fast (and efficiently) up to to 80% or so, but then the remainder is difficult to get in and goes really slowly. I think Nokia has designed it such that in "emergency charger" mode you always stay in the "efficient" region and don't try to charge the battery to the full capacity unless you're on a mains charger.

A proper battery expert can probably tell you that I'm completely wrong and talking out of my a**, but that's the way I understand it. :-)