AFAIK, and battery experts can correct me if this is wrong, nickel iron
batteries have a few weaknesses.
One is mediocre charge efficiency. Their gassing voltage is low, so a fair
bit of the energy put into them goes into breaking down the electrolyte's
water into hydrogen and oxygen.
Also, as that suggests, they need really good ventilation to be safe.
They're not particularly high in specific power, either.
However, they do have a reputation for very long cycle life.
If I'm not mistaken, the "metal" in nickel metal hydride batteries is iron.
So you could say that in a way, Edison's batteries have actually been quite
It's just that NiMH haven't much found their way into EVs. I don't think
that's because of any particular failing, rather it's thanks in no small
part to the GM/Texaco/Cobasys NiMH patent encumberance. Not that I mean to
absolve any of those corporations, but it's too bad that Stan Ovshinsky
wasn't more canny in dealing with GM.