AVR-Chat

Hi guys,

I am designing a university project, a hand-held printer using the 
AVR and a small thermal printer. For portability I want to use 4 x 
2300mAh AA batteries in serial/parallel to provide me with 3V.

The printer runs on 5V but consumes over 3.5A peak, so I require a DC-
DC converter circuit (or at least a starting point) to provide 3V at 
5A peak.

Has anyone designed anything like this, or can give me some advice? 
Maybe someone has an idea for a better battery for me to use?

Cheers
Col