The active materials are held in nickel-plated steel tubes or perforated pockets.

It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated.

[9][10] Some examples are London underground electric locomotives and New York City Subway car – R62A.

[14][15][16] The ability of these batteries to survive frequent cycling is due to the low solubility of the reactants in the electrolyte.

The formation of metallic iron during charge is slow because of the low solubility of the ferrous hydroxide.

[7] Nickel–iron cells should not be charged from a constant voltage supply since they can be damaged by thermal runaway; the cell internal voltage drops as gassing begins, raising temperature, which increases current drawn and so further increases gassing and temperature.

The half-cell reaction at the positive plate from black nickel(III) oxide-hydroxide NiO(OH) to green nickel(II) hydroxide Ni(OH)2 : and at the negative plate: (Discharging is read left to right, charging is from right to left.

[7] The voltage required to charge the NiFe battery is equal to or greater than 1.6 volts per cell.

Jungner discovered that the main advantage over the nickel–cadmium chemistry was cost, but due to the lower efficiency of the charging reaction and more pronounced formation of hydrogen (gassing), the nickel–iron technology was found wanting and abandoned.

Many of the original manufacturers no longer make nickel iron cells,[7] but production by new companies has started in several countries.

The active material of the battery plates is contained in a number of filled tubes or pockets, securely mounted in a supporting and conducting frame or grid.

The grid is a light skeleton frame, stamped from thin sheet steel, with reinforcing width at the top.

The elements must remain covered with electrolyte; if they dry out, the negative plates oxidize and require a very long charge.

The tube retainers are made of thin steel ribbon, finely perforated and nickel-plated, about 4 in.

The retainer pockets are made of thin, finely perforated nickel-plated steel, of rectangular shape, 1/2 in.

The iron oxide, in finely powdered form is tightly rammed into these pockets, after which they are mounted into the grids.

[18] The electrolyte does not enter into chemical combination to perform the functions of the cell, acting as a conveyor.