So they figured out how to overcharge a nickel-iron battery. That was a problem with those old batteries, they were pretty tolerant to overcharge, but they gassed out really bad, and you would have to replace the water lost. A dry cell at 1.56 volts is able to overcharge a nickel-iron cell at 1.2 volts, which happens to be close to the voltage required to split water into hydrogen and oxygen.
So is this a closed system, by which both the hydrogen and the oxygen would be captured and used to fuel an internal combustion engine?
Very interesting thing to notice. The reinventing of wheels via refinements of existing phenomena seems to happen a lot. Reversing things seems to be especially useful!