Cadmium itself is the issue, so depending on its application depends on the timescale. Ed seems to know what hes on about there so thats good enough for me.

You might want to speak to the stinger team, or the draven team. As far as I am aware, they both use F call NimH, and the big nipper team use C (or is it sub c) NiMH (bet Im wrong and they are NiCad now!!)