Systems+Engines

Sulfation surprise

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"The two group 27 batteries on my boat are both four years old. After charging, all cells have a specific-gravity reading of 1.225 +/- 0.005 and about a 75 percent charge. Hoping to improve the readings, I have been charging at 16 volts and 1 amp. After several days, the cells read 1.260 +/- 0.005. Is this a sign of sulfation?"

-- Roger A. Karmes, North East, Maryland

Nigel Calder replies: The short answer is yes. The 1.225 readings are low for a fully charged battery and represent about a 75 percent state of charge on a new battery. The 1.260 reading is close to what you’d expect to see on a fully charged new battery. This leads me to think that you’ve probably driven some of the sulfates back into service and into the acid solution, raising its specific gravity. If this is what has happened, the process will have damaged the batteries’ structure by corroding the grids. If these were not expensive batteries, four years is not a bad service life and you might want to replace them soon. If they are good-quality deep-cycle batteries, they can tolerate the grid corrosion, and chances are good that they have several more years of useful life in them.

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