When you get the electrolyte levels above the all the plates, I would
suggest discharging each of the cells slowly using a light bulb or some
other gentle load. (Or a nifty electronic cell/battery cycler, like a
Cell Pro https://www.electrodynam.com/store/product241.html or something
like it.)
Get them all below 0.4 volts. Then charge them up. This will help to
"reset" the NiCads and remove the stubborn "stale charge" that they have
from remaining dormant for many months.
You might have to do this more than once.
This has also be called the "memory effect", but in the industry, it is
universally called "stale charge." In a nutshell, the paste on the
charged plates anneals over time. The fluffy white snow-like
small-crystalline substance changes into larger crystals as time goes
by. The large crystals don't readily react as do the much smaller
crystals. This makes essentially two cells inside one cell. The first
fluffy crystals offer low resistance and higher voltage, and thus easily
discharge. They leave the large crystals behind as they have a higher
resistance. The longer they stay in place, the larger they grow.
To remove the large crystals and put them back in the electrolyte, you
need to _slowly_ discharge the cell to zero state of charge. This will
"cycle up" the cells to as best as they can be.
All types of cells exhibit stale charge. Some chemistries, like Li-Ion,
only exhibit a very small effect, but is is none-the-less there.
Bill D.
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