Figured I'd throw this to the list as analogue design is really not my 
forte.
I have a small device I'm designing that has 2 (smallish, 350mah) lipoly 
batteries in it, I need to keep it with 2 cells because I'm planning to 
pull 18W from them (for about 3 minutes).
I am going to have an AVR in it talking to the host via USB so its not a 
problem asking for the requite power etc.

Ideally I would like a chip that takes ~4-5V in and charges and balances 
2 lipoly cells and reports stats over some form of serial.

Failing that I am thinking a boost converter controlled by the AVR and a 
bunch of analogue gubbins to measure current and level shift the "high" 
battery voltage. My biggest issue here is the design of things like 
level shifters and the like, I'm thinking some kind of differential amp 
with a gain of 1 might do the trick?

The option I am currently favouring but which feels the worst is an off 
the shelf 5V-12V boost converter followed by a pair of single cell 
lipoly charger IC's with the upper chips gnd floating on top of the 
lower batteries V+. Basically the lower battery charger gets 12v and the 
upper one gets 12v - vbat of the lower cell.
I can see a number of pitfalls to this however and it really isn't that 
elegant.

So any advice, leads or pointers on how to achieve my goal would be 
gratefully received.
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