[If I were you, Iwould look at some NIMH D cells.] The nice thing about gell cells is that they come in a large variety of capacities, already put together in nice modular form. No fiddling with 10 cells in series as with NiCd or NiMH (which is NOT the best way to charge NiMH, as far as I've heard.) No fiddling with large numbers of Li-poly cells in parallel/series to get capacity. A pre-packackaged BATTERY with well-understood charging characteristics and no fancy electronics required. And they're pretty cheap, too, thanks to economies of scale in alarm systems, emergency lighting, and ... cars and such. And they have a pretty good lifetime. They're just, you know, made of LEAD. NiMH D cells will run you $8 to $15 each, Li-poly is expensive as well. By the time you build your 16V pack, you'll have spent near the $200 a new laptop battery would cost you, and who knows whether it will last any longer or not (lifetime wise, not per-charge-wise.) (By the way, most NiMH and NiCd "D" cells are actually C-capacity cells inside a D-sized case (courtesy of "consumer reports".) A state-of-the-art D NiMH had about 9AH capacity... (www.aspencer1.com) (wow, looks like "Energizer ACCU rechargable D cells are even smaller than that. 2200mAH, which is only slightly above what AAs can deliver. (A good C cell seems to be about 4500mAH.) BillW -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics