Hi;
I'm no Oracle, but there are a few things about the N-Cells that are known by many of us.
They are available as Alkaline, NiCad and NiMH, having the same internal characteristics as the other Alkaline, NiCad and NiMH batteries, except for the capacity (mAH) that varies from one type and brand to another. You may also know about it, but it's never worth mentioning: Alkalines are not rechargeable, NiMH and NiCads are. I remember I saw and used some regular type N-cells a long time ago, but they did not keep my HP41C working for long times.
About toxicity, all known cares for disposability and handling must be taken into account because chemicals are strictly the same.
Among us in here, there is one contributor that seems to be the one who deals with batteries for more time, and he knows about brands and types. If I am not wrong it is Glyn, and maybe we are lucky having his comments and explanations about this subject (if I am not wrong, he is a representative or works with batteries, something like this). And he writes too well, easy explains every aspects and details as much as needed. As I am a foreigner, I believe he has one of the best English writing I've ever read before.
Not so much of help, but a few info. Hope it helps a bit.
Cheers.