Howdy! my quick 2cents on this note. From my small amount of study, it apear's the NiFe batteries traditionally utilize KOH solution as the electrolyte.
I have been working with very strong KOH (leached from from oak wood ash) for many years buck-skinnig animal hides. It is not *particularly* dangerous in my experience. I have had my skin exposed to strong KOH solutions of ~pH9 and nothing but a dryness (like dishpan hands) occured. More or less the same as if you get Portland Cement on yourself. Not great, but not *particularly* dangerous in my estimation/experience.
Also, KOH can be quickly neutralized with common vinegar. Either white distilled or apple cider. I know that we always have lots of vinegar around the farm. Either purchased or made from apple cider.
KOH is also endogenic. it comes from the land and the land knows what to do with it. It can be easily and safely treated by dillution with water (no need to nuetralize) and be applied to fields/gardens as a Potash ammendment. That is how I handle my solutions and the pasture I've been speading it on loves it.
So I'm not sure I'm doing this right but here's my 2 cents. KOH is a better option for NiFe batteries because it doesn't destroy the annode or cathode. You can fully deplete these batteries and come back in 10 years, rinse them out, replace the koh with new solution and charge em right up. There is no acidic destruction of the innards, so it's a battery (when done with KOH) that even your grandkids can use.
