I dunno how long those U/S nicad cells will last you, Mouse, but I guess it's a good (free!) start.
(I work in the aviation industry, and spent a bit less than a year working in a NiCad battery shop... (holy boring job, batman!))
Unfortunately I'm no longer in a position to snag dead cells like that, otherwise I'd probably do the same thing. A friend once got enough cells to build up a small (yet still heavy) pack to power an awesome coilgun he'd built at home. That was fun!