What's your battery shelf-life experience?
While looking for more batteries during a recent power failure, I came across some D-size alkaline cells in the back of a drawer, in their original package (see photo) with the price and store name sticker. I looked at the "best if used by" date and it said "2014", so I figured I was all set. But then I took a closer look and saw the date was 2004, not 2014—oops! I thought the batteries would be nearly useless.
Since I had nothing to lose and I needed more batteries, I figured I would try them. They were physically in good shape, with no corrosion or leakage. I had no time nor inclination to follow standard engineering protocol and measure the open-circuit, no-load voltage. I just popped them into a conventional incandescent-bulb flashlight (not a high-efficiency LED unit).
I was very pleasantly surprised to find the flashlight came on full brightness. Of course, that doesn't tell me how much underlying capacity remained in the batteries (amp hours) but still, to get full brightness from old, albeit unused alkaline cells, there has to be some reasonable amount. It also tells me that their internal resistance was still pretty low, which is both surprising and a good thing, since increase in that parameter is not only a sign of aging, but a major contributor to reduction in terminal output voltage under load.
I came to this conclusion because unlike lithium batteries, whose terminal voltage remains relatively flat even as they discharge, alkaline cells have a steady drop in voltage versus capacity. So I wouldn’t have seen full-output voltage unless the remaining amp-hour capacity of the cells was at least reasonably good.
Why should we care about shelf life? Shelf life is not only for batteries which are not in use. With many of today's extremely low-drain applications (milliamps or even microamps), the battery is close to being unused even in actual use, so it is an important and relevant factor.
What's been your experience with shelf life of various cell chemistries, such as lead acid, alkaline, lithium, and even old-fashioned carbon zinc? Have you used them near the end of the official life? What about using them way beyond that date?
And a special note to the folks at Duracell: perhaps your Duracell bunny mascot needs a break. If you are looking for a credible, non-celebrity substitute spokesperson to testify about the long shelf life of your products, I'm available. My rates are modest, and I can assure you there won’t be any scandals associated with me, unlike with some other celebrities!