Q. I just opened my battery-operated alarm clock and found a badly corroded AA battery. Even though the date on the battery read MAR 2014, it was covered in white crystals. Are those crystals dangerous to touch?—Alex Newberry Sarasota, FL
A. As batteries discharge—either through usage or gradual self-discharge—the chemistry of the cells changes and some hydrogen gas is generated. That increases pressure in the battery, which either ruptures the insulating seals at the end of the battery or the outer metal canister, or both. In addition, as the battery ages, its steel outer canister may gradually corrode or rust.
Alkaline batteries are prone to leaking potassium hydroxide, a caustic agent that can cause respiratory, eye, and skin irritations.
You can reduce the risks by not mixing battery types in the same device, and by replacing all of the batteries at the same time. You should store batteries in a dry place and avoid extremely high temperatures. As another measure, remove the batteries when you store the device.
—Consumer Reports
This article appeared in the February 2014 issue of Consumer Reports magazine.
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