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Battery leaks was an issue in the 80s and 90s, and since quality and innovation is constantly improving, I thought battery leak might be slowly going away. But I found that even nowadays, name brand alkaline batteries still leak after a while, even if originally concealed in a tight package of the metal shell. Is it true that the chemical in an alkaline battery inherently expands in volume over time, and make the alkaline battery leak issue unavoidable?

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    $\begingroup$ I'm betting that the alkaline solution just slowly eats the casing. $\endgroup$ – Ben Norris Aug 17 '12 at 16:06
  • $\begingroup$ Nope, it eats zinc electrode. Wikipedia article about alkaline batteries has good discussion on the subject $\endgroup$ – permeakra Aug 17 '12 at 16:59
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    $\begingroup$ @permeakra The wikipedia article is not bad, but one key feature is missing: Where is the KOH? Is it mixed with the Zn? Is it mixed with the manganese (II) oxide? KOH reacts with amphoteric oxides, like manganese (I) oxide and zinc oxide, which form as the battery discharges. I'm not sure where the hydrogen gas mentioned comes from; hydrogen usually forms in acidic redox. I would guess that water forms, and expands and/or vaporizes. $\endgroup$ – Ben Norris Aug 18 '12 at 12:09
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    $\begingroup$ $KOH$ is electrolyte here, it has to have contact with both $MnO_2$ and $Zn$ . $Zn$ slowly reacts with solutions basic enough, the reaction is $Zn + 2KOH + 2H_2O = K_2[Zn(OH)_4] + H_2$. The reaction is slow and may be slowed even further by slowing diffusion in electrolyte solution, but not stopped. When battery is discharged (but not self-discharged), the reaction is different and no hydrogen produced. When battery cannot be discharged externally (too low voltage to give some current) it still can self-discharge and hydrogen produced will tear case apart if any Zn remains in battery. $\endgroup$ – permeakra Aug 18 '12 at 14:33
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    $\begingroup$ @permeakra That is a pretty good explanation. You should turn it into an answer. $\endgroup$ – Ben Norris Aug 19 '12 at 13:48
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The reason for leaks in alkaline batteries is that as batteries discharge — either through usage or gradual self-discharge — the chemistry of the cells changes and some hydrogen gas is generated. This out-gassing increases pressure in the battery. Eventually, the excess pressure 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 (in alkaline batteries there is some potassium hydroxide, a very strong base) or rust, which can further contribute to containment failure. (see http://en.wikipedia.org/wiki/Alkaline_battery#Leaks )

I also found this online :

Heat is the biggest culprit. Storing your flashlights under the seat of your car, or in direct sunlight will cause the batteries to leak. The reason they leak is because they are filled with a chemical paste of which the liquid portion is composed of a base called Potassium Hydroxide. When the batteries get hot, the paste inside expands, and forces chemicals out of the seals in the bottom and top of the battery. [...] Regardless of the brand you buy,[...] all batteries will leak eventually, so if you don't use the flashlight for extended periods of 3 months or more, remove the batteries, or change them out every couple months. (from here)

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