I actually built this over 5 years ago, when there werent any good li-ion solutions on the market. I just got back into taping and bought some new cells for $1 on ebay, so it appears to still be a good deal for homebrewers
http://www.simplefuels.com/tapergeek/liion.htmscroll down to the bottom for the updated dual-voltage version. I used this with a v3+ad2k for a long time, and stepping the v3 down to 6V made a huge difference, the rig would run for an extra 45min-1 hour. (I think I would get 5 hours out of those units with this). I also used to use another pack with the targus adapter to run my sony u3 laptop for 4+ hrs. this pack would run the ad2k alone for over 7 hours
ebay link to $1 cells ($5-$7 after shipping):
http://cgi.ebay.com/NEW-Toshiba-Satellite-Batteries-PA2492U-PA2494U-D_W0QQitemZ170080505314QQihZ007QQcategoryZ60260QQrdZ1QQssPageNameZWD1VQQcmdZViewItemI just got 4 of these and tested them over the weekend. I had to manually get the pack voltage up over 11V before trhe charger would cxharge them, but they were properly stored at 7V just like a good li-ion should, and appear to have full capacity.
The pa2493 chargers are a little harder to come by, but they do show up on ebay from time to time