What is the basic theory behind storing batteries in the refrigerator? Supposedly it extends their shelf-life, but if that is the case, why?

Years ago, I believed that batteries stored in a cold freezer/fridge would last indefinitely. My December, 1999, Consumer Reports says that it produces only marginal shelf life over room temperature storage. They probably did the tests to back this up. But I still believe that high heat can shorten life.

the battery works through a chemical reaction that pumps electrons across it. One of the factors that determines how a chemical reaction proceeds is temperature. If you lower the temperature, you tend to lower the speed of the reactions. And so the battery will last a bit longer.

Chilling/freezing batteries may have had more relative benefical effect years ago, before the more modern chemical concoctions. Since batteries in days of yore didn’t last all that long (compared to today’s), the “marginal” increase seen today may have seemed significant at the time.