Nickel iron electrolyte is a mixture of potassium hydroxide (KOH) and Lithium hydroxide (LiOH)
They should both be high quality grades and not some “off the shelf” stuff.
I have a small set of nickel iron cells that are 70 years old that I believe at one time where used for powering up a radio. They are 37.5 Ah battery that I turned into a 12V battery. I use them to recharge small electric items such as my cell phone, AA and AAA rechargeable batteries etc. Indeed they work like new after so many years.
Iron Edison:
I believe the cells you are selling are not made identical to the original nickel iron battery and I correct? Do you believe that your cells will last as long as the original cells and what so what makes you think that when materials today generally are not what they used to be when Thomas Edison started making his cells.