Building a USB Battery pack for Nintendo 3DS

Hi everyone,

I'm not a total stranger to this site, just my 1st time signing up and posting.
I'm asking for some advice for building a USB Battery pack, I've already got my prototype for a simple pack using 3x AA Dry cell Batteries, i know some things about electronics already, but i need a little more advice about Undervolting and Overvolting.
Using the Dry cells I have 3 batteries which will give me 4.5v, my intention is to use 4 AA NiMH cells, and those are 1.2v which will give me 4.8v, and the 3DS has a 4.6v requirement for a charger, i have a few other questions too.

i'm worried these might damage the 3DS in the long term, would the 0.1v undervolt or 0.2v overvolt actually damage my device with the DC Current, or would it just draw what it needs?
Would i be better to add in a voltage protection circuit, and while i'm at it, are there any circuit diagrams for building in a Charger for the NiMH Batteries in the unit?

Thanks for any help in advance, and will appreciate the feedback