If those are Nickel Iron cells from the Edison Battery Company in Orange, NJ
You should be able to see the metal engraving on the lid caps. He used metal (steel) cases rather than plastic (right up to 1972 when Exide corp bought out the company and ceased NiFe battery production). The metal cases were isolated from each other when the cells were grouped in series by using an ebonite-tar coating (the black outside coating)
They charge at 1.7v per cell, float at around 1.4v p/c and have a NOMINAL cell voltage of 1.2v
They should ideally be charged at the 7-Hour rate, Edison makes a big note of this is some of his patents on the cells.
Nickel-Iron was originally invented by a brilliant electro-chemist called Ernst Waldemar Jungner, from Sweden, Edison did what he did best and “built on” the invention and patented it in the USA in late 1890’s to early 1900’s.
He did make some notable improvements on the original invention though, and the use of Nickel Oxyhydroxide at the key active compound on the Positive electrode increased cell capacity and cell voltage over the use of straight Nickel Hydroxide.
His notes comment on this process being able to effectively restore almost the entire amp-hour capacity (a feature that is missing in the new versions of the NiFe batteries that are coming out of China in recent years in plastic cases).
The KOH electrolyte doesn’t take part as a reactant during normal operation.
Upon normal discharging (from a fully charged state) the process that follows is:
Fe(s) + NiOOH(s) + 2H2O <=> Fe(OH)2 + Ni(OH)2 + H+
Then a further decomposition reaction of the Iron electrode (at a half-equation voltage of approximately 0.9v) of;
3Fe(OH)2 + 2NiOOH <=> 2Ni(OH)2 + Fe3O4 + 2H2O
The - iron electrode usually ends up becoming a form of Iron oxide, and this is fully reversible during the next charge as the iron undergoes reduction back to straight metallic Fe(s).
The cells can sit empty and dry for years and be revitalised back to near full capacity.
They have a low energy density (approx. 30-50Wh per Kg) which is close to Flooded Lead Acid (40Wh per Kg), but their extremely long life span (25 years + before needing the “refresh charge” to be performed due to the iron carbonate build up) and their potential of being restored again many times over makes them extremely vital.
If you have the opportunity to play with these old cells, I highly recommend it.
You can learn everything you need to learn about managing them and their chemistry from reading the patents of both Jungner and Edison, simply do google patent searching for both names and look for “Alkaline rechargeable / secondary battery patents”.
