Just a few links for the hardware shopper -
Batteries (for the external battery stack):
http://www.bgmicro.com/BAT1094.aspx
or
http://www.bgmicro.com/ur18650f-2000...-by-sanyo.aspx
(not sure if those are 'AA' size but they look like it in picture and I don't know if those are 1.2v single cell, or a cell stack)
Battery holder (for the external battery stack):
http://www.bgmicro.com/battery-holde...lder-tabs.aspx
or
http://www.bgmicro.com/battery-holde...terminals.aspx
Those Li-Ion batteries **do have** enough storage capacity to run the Kindle (and so do the Ni-MH batteries, but may not be able to supply the peak current required by the 3G modem).
Total cost: about $8
Battery charger for 1 or 2 of the Li-Ion batteries:
http://www.bgmicro.com/18650-battery...-with-led.aspx
Another $8
(The charge specs. suggest that the 18650 is a 3.6v, 3-cell, device).
Ah, well, those folks have e-mail address and telephone number to clarify the above unknowns.
(Personally, I have to lockup my credit cards before going to that site.)