How to rejuvenate a lead acid battery

You should get quite a wide range of information doing a Google search using your question:
High Potassium Foods
You will get returns like these:and much more...

15 Foods That Are High In Potassium

High Potassium Foods Topic Overview


http://www.everydayhealth.com/pictures/foods-high-in-potassium


Top 10 Foods Highest in Potassium You Can Miss

Bigger crystals will crystallized from purest material. You may be have purify KCl, use pure and filtered before using water/solvent, protect beaker or used vessel from air dust.

You will need to look around for a small tank (about the size of a 5 gallon bucket) that connects to the softener by a small tube, 3/8 tube maybe, if there is a small tank, and this system was neglected, it WILL have trace evidence of a dark brown almost black stain on and around the tank...if not...DO NOT pour any KmNo or Potassium Permanganate into the brine tank..either you or your service man will be using foul language if you do ! ;o

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Try Re-Conditioning the battery first. Full procedure at: ysuusy.com/easybatteryfix.html
"Cordless Power Tool Batteries and other batteries that contain Nickel Cadmium (NiCd) Cells can be Re-Conditioned to perform as well as new or even better than new. Proper maintenance after the procedure will insure years of usable life.
The First and most common procedure for Re-Conditioning a NiCd cell is by using a Technique called "VOLTAGE SURGING". Over time the crystals within a NiCd cell begin to combine and get larger. This causes them to loose capacitance and also break through the inner seals of the cell.
Surging the NiCd cell using a higher voltage causes the crystals within the NiCd cell to shatter and become smaller. These smaller crystals have a greater surface area and therefore contain a greater capacitance for energy. "